1 examination 1 chemistry 3b . name:____ sid #: print...

1

EXAMINATION 1 Chemistry 3B

Name:__________________________ SID #:______________________ Print first name before second! Use capital letters! Peter Vollhardt February 23, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 17 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (30)

II. ______ (30)

III. ______ (50)

IV. ______ (50)

V. ______ (40)

VI. ______ (30)

VII. ______ (20) Total:

(250)

2

I. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC

rules. Indicate stereochemistry where necessary (cis, trans, R, or S). a.

I

Br

CHO

b.

O

c. R-4-Methyl-2-cyclohexenone

d. Meta-(1-methylethyl)(methoxymethyl)benzene

3

e.

II. [30 Points] 1-Methylthio-4-nitrobenzene A undergoes preferential electrophilic attack by E+ to give only one of the two products shown.

NO2

SCH3

12

3

4

E+

-H+

NO2

SCH3

E

or

NO2

SCH3

E

A

a. Which one? Mark the box below your choice with an X. b. Write the resonance forms of the intermediate formed on attack of E+ at:

C-2:

Four resonance forms

4

C-3:

Three resonance forms c. Circle (in your answers above): a. the most strongly contributing resonance form of the attack at C-2 and b. the least contributing resonance form of the attack at C-3. III. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer. a.

+ HCl Thermodynamic product

b.

Δ A cyclobutene

H3C

H3C

CH3

OCH3

5

c.

+

CN

CN

d.

hν

HH

A hexatriene isomer of product.

e. K+ -OC(CH3)3

CH3

CH3

13C NMR: 7 lines A salt; 13C NMR: 4 lines f.

NO2

OCH3

ClSO3,H2SO4

6

g.

OH

OH

CH3CCH3

OH+

-H2O+

13C NMR: 4 lines

h.

Cl, AlCl3

O 1.

2. Zn(Hg), HCl, Δ

i. 1. P(C6H5)3

2. CH3Li 3.

O

I

7

j. H2NNH2, Δ, and

O

IR Spectrum of product : A hydrocarbon

4000 3000 2000 1500 1000 500 cm-1

IV. [50 Points] Treatment of acetal A with conc. nitric acid and H2SO4 led to unknown B. The IR and NMR spectra of this product are shown below.

HOH

O O

HO3S

B (unknown)

1. HNO3, H2SO42. H2O, H+, Δ

A

8

a. After consideration of the spectral data, write the structure of the product in the box below. Structure of unknown b. Interpret the spectral data as requested in the spaces provided. 1. IR Spectrum

Confirm or rule out the presence or absence (circle one) of the following bonds. Enter an approximate expected stretching frequency in the box. ν~ (Csp

2–H) is: present absent at

cm-1

9

ν~ (O–H) is: present absent at

cm-1

ν~ (C=O) is: present absent at

cm-1

2. 13C NMR Spectrum (these are all single lines; ignore the seeming splitting of some).

A

D

B C

ppm The proton-coupled spectrum leaves the singlets for B, C, and D unchanged.

10

Draw your suggestion for the unknown in the box below and label the types of carbon atoms A, B, C, and D, giving rise to the corresponding signals in the spectrum. For the assignment of B, C, and D, consider that the order of chemical shifts parallels roughly the order of electronegativity of the attached atom. 3. 1H NMR Spectrum (for expanded sections, see next two pages).

A B C D E ppm

11

The signal due to protons A disappears in D2O solvent.

B

A

ppm

C

12

ppm

D E ppm Draw your suggestion for the unknown in the box and label the hydrogens A, B, C, D, and E giving rise to the corresponding signals in the spectrum.

13

V. [40 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need.

NO

+

NH2

H

H

H+

a.

14

b.

CH3CCH3

O

+ CH3COOH

O

CH3COCH3

O

+ CH3COOHH+

Work from left to right in the following spaces. There is much more space than you will

need.

15

VI. [30 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms!

a. Here, you may use any additional organic or organometallic reagents to effect your conversions.

OH

Work from left to right in the following spaces. There is much more space than you will need.

16

b. Synthesize compound A using only the materials shown and no additional reagents. , , H2NNH2

O

O

N

N

A


17

VII. [20 Points] Place an X mark in the box next to the most accurate statement. a. The equilibrium constant for hydration of 1, 2, and 3 increases in the order

F3C H

O

CH3

CH

O

H3C CH3

O 1 2 3 1, 2, 3

3, 2, 1

2, 3, 1

3, 1, 2 b. Circle the compounds which are aromatic

:

The End

1


Name:__________________________ SID #:______________________ Print first name before second! Use capital letters! Peter Vollhardt September 28, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 20 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (30)

II. ______ (30)

III. ______ (50)

IV. ______ (60)

V. ______ (30)

VI. ______ (30)

VII. ______ (20) Total:

(250)

2

I. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC rules. Indicate stereochemistry where necessary (cis, trans, R, or S).

a.

Cl

Br

b.

O

F

c. S-4-Methyl-2-cyclohexenone

d. 4-Methyl-3-nitrobenzenecarbaldehyde

3

e.

II. [30 Points] Compound A undergoes preferential electrophilic attack by E+ to give only one of the two products shown.

CH3

12

3

4

E+

-H+

E

CH3

NO2

or

CH3

E

A

O2N NO2

5

O2N O2N NO2

a. Which one? Mark the box below your choice with an X. b. Write the resonance forms of the intermediate formed on attack of E+ at:

C-4:

Three resonance forms

4

C-5:

Three resonance forms c. Circle (in your answers above): a. the most strongly contributing resonance form of the attack at C-4 and b. the most strongly contributing resonance form of the attack at C-5. III. [50 Points] Add the missing components (starting materials, reagents, or products) of the

following reactions in the boxes provided. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer.

a.

OS

O

O

CH3OH

Solvolysis

Thermodynamic product

b.

hν

C(CH3)3

C(CH3)3

5

c.

+ O

O

O

d.

Δ

CH3

CH3

An octatetraene isomer of product.

e.

NBr

O

O

ROOR+ NH

O

O

+

6

f.

F

CH3

SO3, H2SO4

NH

O

g.

OH

O

H+, CH3OH

IR spectrum of product :

7

h.

CH3O

CH3

Br2, FeBr3

Monobromination

i.

1.

2.

3.

SO3H

NH2

8

j.

O

HSSH

1.

2.

Mass spectrum of product :

9

IV. [60 Points] Heating compound A with acetylene gas under pressure generated the unknown B. The complete spectral data for this product are shown below in the sequence : 1. 1H NMR , 2. 13C NMR , 3. Mass , 4. IR , 5. UV. Δ

OCH3

OCH3

Cl

H C C H+ B (unknown)

A a. After consideration of the spectral data, write the structure of the product in the box below.

10

1. 1H NMR Spectrum (for expanded section, see bottom spectrum).

C

A B

ppm

BA

9 Hz

ppm

11

b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, and C giving rise to the corresponding signals in the spectrum. Consider resonance in your assignments of A and B. 2. 13C NMR Spectrum (these are five single lines).

C

D

E

B A

ppm

12

The proton-coupled 13C NMR spectrum leaves the singlets for A and B unchanged, but shows that each of the carbons giving rise to signals C and D are attached to one hydrogen, while the carbon due to E bears three hydrogens.

Draw again your suggestion for the unknown in the box below and label the types of carbon atoms A–E giving rise to the corresponding signals in the spectrum. For the assignments of A versus B and C versus D, consider the effect of electronegativity of the attached atom and the effect of resonance, respectively.

13

3. Mass spectrum

a. Clearly mark on the spectrum the molecular ion as “M+”. b. In the box above the fragment ion m/z = 199, indicate the molecular piece that has fragmented from M+, e.g. “Cl”, or “CH3O”, or “CH3CH2”, or ?

14

4. IR Spectrum


2–H) is: present absent at cm–1

ν~ (Csp–H) is: present absent at

cm–1 ν~ (C≡C) is: present absent at

cm–1

15

nm

5. UV spectrum Place an X mark into the box next to the most accurate statement. The spectrum depicts a nonconjugated compound. The spectrum is that of a colored compound. The unknown is aromatic. The λmax is at 300 nm.

16

V. [30 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need.

a. OO

Catalytic H+

17

b.

Cl3CCH + H2OH+

O

C OH

OH

H

Cl3C Work from left to right in the following spaces. There is much more space than you will

need.

18

VI. 30 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms!

a. OCH3

H3C CH3

OCH3

H3C CH3

NH2


19

b. Synthesize compound A from any materials containing six carbons or less.

CH3

CH2OH

CH3

A Work from left to right in the following spaces. There is much more space than you will need.

20

VII. [20 Points] Place an X mark in the box next to the most accurate statement. a. The electron donating power of benzene substituents 1–4 increases in the order −CH3 −OCH3 −NO2

NCH3

CH3

1 2 3 4 1, 2, 3, 4

4, 3, 2, 1

4, 2, 3, 1

4, 1, 2, 3 b. Circle the compounds which are aromatic

:

:

The End

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1


Name:__________________________ SID #:______________________ Print first name before second! Use capital letters!

GSI (if you are taking Chem 3BL): ______________________ Peter Vollhardt October 2, 2008 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 20 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (30)

II. ______ (30)

III. ______ (50)

IV. ______ (60)

V. ______ (30)

VI. ______ (30)

VII. ______ (20) Total:

(250)

2

I. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC rules. Indicate stereochemistry where necessary (cis, trans, R, or S).

a.

Br

b.

O

c. (S)-3-Methylcyclohexanone

d. trans-4-Bromo-2-oxo-3-butenal

3

e.

II. [30 Points] Compound A undergoes preferential electrophilic attack by E+ to give only one of the three products shown.

OCH3

12

3

E+

-H+ or

OCH3

E

A

NO2

4

NO2

CH3

5

6

CH3

OCH3

NO2

CH3

E

OCH3

NO2

CH3

or

E

a. Which one? Mark the box below your choice with an X. b. Write the resonance forms of the intermediate formed on attack of E+ on A at:

C-3:

Three resonance forms

4

C-5:

Three resonance forms C-6:

Four resonance forms c. Circle (in your answers above) the most strongly contributing resonance forms of the attack at C-3, C-5, and C-6. d. Considering all of the above most strongly contributing resonance forms, which one is the best overall? Redraw it in the box below.

5

III. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Show stereochemistry when appropriate. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer.

a.

OS

O

O

CH3OH (solvent)

Thermodynamic product

b.

hν

CH3

CH3

c.

+ O

O

O

6

d. Δ

CH3

CH3

Product of ring opening

e.

NBr

O

O

hυ+ NH

O

O

+

f.

F

CH3

SO3, H2SO4

NH

O

7

g.

O

H+, HOCH2CH2OH

IR spectrum of product:

h.

CH3O

Cl

Br2, FeBr3

Monobromination

8

i. 1.

2.

3.

SO3H

CH3

CH3

NH2

j.

1.

2.

O

H

9

IV. [60 Points] An attempt to effect allylic bromination of A generated the unknown B. The complete spectral data for this product are shown below in the sequence: 1. 1H NMR, 2. 13C NMR, 3. Mass, 4. IR, 5. UV.

H3CO

O

HNBr

O

O

+

A

B (Unknown)

a. After consideration of the spectral data, write the structure of the product in the box below.

10


A B C D 1H 2H 2H 3H B C

ppm

11

b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, C and D giving rise to the corresponding signals in the 1H NMR spectrum on p. 10. Consider resonance in your assignments of B and C.

2. 13C NMR Spectrum (these are six single lines).

E

C F

A B D

ppm

12

DEPT spectra (don’t worry if you don’t remember what that is) shows that the carbons giving rise to signals A, C, and E are attached to one hydrogen each. Signal F is due to a carbon with 3 attached hydrogens. Signals B and D are associated with carbons without any bound hydrogens.

Draw again your suggestion for the unknown in the box below and label the types of carbon

atoms A–F giving rise to the corresponding signals in the 13C NMR spectrum on p. 11. For the assignments of B versus D and C versus E, consider the effect of electronegativity of the attached atom and the effect of resonance, respectively.

13

3. Mass spectrum Atomic weights of all the elements in the reaction on p. 9: H 1; C 12; N 14; O 16, Br 79 and 81 (1:1 isotope ratio). Caution: Not all of these elements are incorporated in the product. 136 a. Clearly mark on the spectrum the molecular ion as “M+” and the base peak as “B+”. b. In the box above the fragment ion m/z = 135, indicate the structure of this fragment.

14

4. IR Spectrum

Confirm the presence or absence (circle one) of the following bonds. Enter an approximate expected stretching frequency in the box. ν~ (Csp


ν~ (Csp


cm–1 ν~ (C=O) is: present absent at

cm–1

15

5. UV spectrum

nm Place an X mark into the box next to the most accurate statement.

The spectrum depicts a nonconjugated compound. The spectrum is that of a colored compound. The unknown is aromatic. The λmax is at 300 nm.

16

V. [30 Points] Write detailed stepwise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need.

a.

ONH2

Catalytic H+ N

17

b.

O

O

O

OH

O

O


need.

18

VI. [30 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products.

a. CH2OH

Caution: You cannot introduce the –CH2OH group directly. Hint: To do so, think alcohol synthesis.


19

b. Synthesize compound A from any acyclic materials containing six carbons or less. Hint: Think Diels-Alder reaction. Caution: Work backwards. What compound must precede A for a retro-Diels-Alder step?

CN

CNH

H

A Work from left to right in the following spaces. There is much more space than you will need.

20

VII. [20 Points] Place an X mark in the box next to the most accurate statement. a. The electron withdrawing power of benzene substituents 1–4 decreases and their

electron donating power increases in the order −CH3 −OCH3 –F −NO2

1 2 3 4 1, 2, 3, 4

4, 3, 1, 2

4, 2, 3, 1

4, 1, 2, 3 b. Circle the compounds which are aromatic

:

:

♫ The End ♫

1



GSI (if you are taking Chem 3BL): ______________________ Peter Vollhardt October 1, 2009 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 15 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (30)

II. ______ (30)

III. ______ (50)

IV. ______ (40)

V. ______ (40)

VI. ______ (40)

VII. ______ (20) Total:

(250)

2

I. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S).

a.

b.

c. (R)-2-Methylcyclohexanone

d. (E)-3-(p-Methylphenyl)but-2-en-1-ol

3

e.

II. [30 Points] Compound A undergoes preferential electrophilic nitration to give only one product.

12

3

HNO3, H2SO4or

NO2

A

CF3

4

CF3

CH3

5

6

CH3

CF3

CH3

O2N

CF3

CH3

or

O2N

a. Which one? Mark the box below your choice with an X, preferably after you have completed questions b.–d. b. Write all the resonance forms of the intermediate formed by attack of E+ (= NO2

+) on A at:

C-3:

12

3

CF3

4

CH3

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures.

4

C-5:

12

3

CF3

4

CH3

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures. C-6:

12

3

CF3

4

CH3

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures. c. Circle (in your answers above) the most strongly contributing resonance forms of the attack at C-3, C-5, and C-6. d. Considering all of the above most strongly contributing resonance forms, which one is the best overall? Redraw it in the box below. 1

2

3

CF3

5

6 4

CH3

5


OH

OH

O a. OH

b.

CH3OH, H+

c.

CH3

CH3

+

CN

CNO CH3 O

Use the stencil above and add all the groups missing from the hashed and wedged bonds.

6

d. Δ

CH3

CH3


e. f.

F

H3C

SO3, H2SO4

OCH3

O2N

7

g.

h.

CH3O

Cl

Br2, FeBr3

Monobromination

1.

2.

3.

i.

8

j.

CH3

H

H

H

CH3

CH3

H

H

H

CH3 Two diastereomers. Add the missing pieces. IV. [40 Points]

a. In the reaction shown, which product is the result of 1,4-addition, and which is the thermodynamic product, respectively? Circle the appropriate answer.

H3C HCl H3CCl

+H3C

Cl

A B

Product of 1,4-addition: A B Thermodynamic product: A B

9

b. Rank compounds 1–5 in order of increasing acidity. Mark the box next to the best answer below.

1, 2, 3, 4, 5 1, 4, 2, 3, 5 3, 1, 5, 4, 2

5, 3, 1, 4, 2 4, 1, 2, 5, 3

c. Circle the compounds which are aromatic:

CH3

CH3

10

d. Rank compounds 1–5 in order of increasing reactivity as dienes in the Diels-Alder reaction:

1, 2, 3, 4, 5 1, 4, 2, 3, 5 3, 1, 5, 4, 2 5, 3, 1, 4, 2 3, 1, 2, 4, 5

11

V. [40 Points] Write detailed stepwise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have!

a.


12

b. Intramolecular Friedel-Crafts alkylation of A provided the expected B, but also 10% of C, suggesting the operation of a competing pathway to the normal mechanism. Propose such a pathway to C. Caution: Do not propose a pathway to B, it will not be graded! Hint: While unusual in this case, what is the normally preferred position of electrophilic attack in naphthalene?


13


a.


need.

14

b. Synthesize compound A from any acyclic materials and any other reagent. Hint: Think Diels-Alder reaction. Caution: Work backwards.

A (racemate) Work from left to right in the following spaces. There is much more space than you will need.

15

VII. [20 Points] Place an X mark in the box next to the most accurate statement. a. Kinetic versus thermodynamic control is present when a racemate is formed in a reaction

the (4N+2) rule overrides the Lewis octet rule

of two isomeric products the less stable one is formed

the reaction requires heat to go to completion

everything happens all at once b. The reactivity of the carbonyl group increases with increasing electrophilic character of the carbonyl carbon

with electron donating substituents

on formation of acetals

on reduction

on going from aldehydes to ketones

♫ The End ♫

1


Name:__________________________ SID #:______________________ Print first name before second! Use capital letters! Laboratory GSI (if applicable): ––––––––––––––––––––––––––– Peter Vollhardt April 6, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 18 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (20)

II. ______ (50)

III. ______ (60)

IV. ______ (40)

V. ______ (60)

VI. ______ (20)

Total:

(250)

2

I. [20 Points] Write a detailed mechanism of the following aldol condensation using arrow

pushing techniques.

O

H

CH3

+

O

NaOH, H2O H

O –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

3

II. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer.

a.

O

H2O, H+

IR: ν~ = 3350 (broad), 1720 cm–1 b.

1.2. CH3OH OCH3

O

SOCl2

Mass spectrum of starting material:

4

c.

Cl

O

H

O d.

NH2

O

NaOH, Br2

e. f.

H

O

COOH

OH

1.

2.

NH2

NH3, NaBH3CN

13C NMR : δ = 208.9, 45.7, 29.8, 17.4, 13.7 ppm

5

g. N

CH3

H

NCH3

NO

h.

CH3HHH3C

H3CCH3

i.

H+, THF

O

+

N

H

IR: No peaks >3010 cm–1

j.

O

O

+ 2 CH3MgBr

6

III. [60 Points] Subjecting acid A to the three step sequence shown below led to unknown B. The mass, IR, and NMR spectra of this product are shown on the following pages.

1. PBr3 2. Br2 3. NH3 (excess) B (unknown)

O

OH A a. After consideration of the spectral data, write the structure of the product in the box below. Structure of unknown b. Interpret the spectral data as requested in the spaces provided, starting on the following page.

7

1. Mass Spectrum Label the molecular ion as “M+” and the base peak as “BP”. Using the partial periodic table on the previous page for atomic weights, draw the structures of the fragment ions at m/z = 148, 120, 91, and 77, respectively, in the boxes below. Draw a “+” charge at the point of the dangling valence in your line structure. m/z = 148 m/z = 120 m/z = 91 m/z = 77

8

2. IR Spectrum



cm–1 ν~ (Csp


cm–1

ν~ (N–H) is: present absent at

cm–1


cm–1

9

3. 13C NMR Spectrum (these are all single lines; ignore the seeming splitting of some).

B

C D

A ppm Draw your suggestion for the unknown in the box below and label the types of carbon atoms A, B, C, and D, giving rise to the corresponding signals in the spectrum. Note that B is a group of four signals, which belong to a group of similar carbon atoms all of which should be labeled “B”.

10

4. 1H NMR Spectrum (for expanded sections, see below and the next page). A,B D E F G

C

ppm

B

A C

ppm

http://www.nd.edu/~smithgrp/structure/hnmrhtmls/hnmrgifs/hnmrmaps/hnmr22.GIF.map�

11

As indicated on the spectra, the signals due to protons A, C, and G disappear in D2O solvent (“exchanges”).

ppm Draw your suggestion for the unknown in the box and label the hydrogens A–G giving rise to the corresponding signals in the spectrum. Note: A and C can be assigned arbitrarily. B corresponds to a group of five hydrogens that can be assigned as such. E and F are due to hydrogens attached to the same carbon and can also be assigned arbitrarily.

12

IV. [40 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need. a.

N

Note: Disregard the mechanism of catalytic hydrogenation.

O

C O

O

H2, Pd−C, ΔN

OH

OO

H

13

b. O

+ Cl2HCl

O

Cl


need.

14

V. [60 Points] Provide a reasonable synthetic route from starting materials to product. Note: Several steps are required, and there may be more than one solution to the problem. You may use any additional organic or organometallic reagents to effect your conversions. Do not write mechanisms!

O

O

O

H2N OCH3

O

a.


15

b.

O

Na+-CNIn 3 steps or less


16

c.

P(C6H5)3

O O

Br


17

VI. [20 Points] a. Name the following molecule according to the IUPAC rules.

O O

O

NH

CH3

H

b. The mass spectrum of 2-propylcyclohexanone is shown below. What is the origin of the large fragmentation peak at m/z = 98? Show your answer in the form of a scheme using e-pushing.

18

The End



Laboratory GSI (if applicable): Peter Vollhardt ______________________ November 2, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 21 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (25)

II. ______ (50)

III. ______ (50)

IV. ______ (45)

V. ______ (45)

VI. ______ (35)

Total:

(250)

Chemistry 3B, Examination 2 Page 2 I. [25 Points] Write the products of the following reactions of the starting material, methyl 3- methylbutanoate.

CH3CH2OH, H+

CH3NH2, Δ

1. CH3MgBr (2 equiv.) 2. H+, H2O work-up

1. LiAlH4

2. H+, H2O work-up

1. 2. H+, H2O work-up

AlH

2

OCH3

O

Chemistry 3B, Examination 2 Page 3 II. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is

assumed to follow each step. It is not part of any answer. a.

NH

, H+

O

Mass spectrum of product::

Chemistry 3B, Examination 2 Page 4 b.

1. HCN

2. H+, H2O

COOHHO

13C Spectrum of starting material:

c. O

Chemistry 3B, Examination 2 Page 5 d.

O

CH3COOH

O

e.

NaOH, H2O, Δ

CH3

O

O

C11H10O

f.

COOH

Br COOH

Chemistry 3B, Examination 2 Page 6 g. H+, CH3OH

O CH3

O

O

C6H12O2

IR spectrum of product :

h. CN CH2NH2

Chemistry 3B, Examination 2 Page 7 i. Cl2, NaOH

NH2

IR spectrum of starting material :

j.

O H N

CH3

H

Chemistry 3B, Examination 2 Page 8 III. [50 Points] Treatment of 2-bromopropanoic acid A with base gave, after work-up with aqueous HBr, mainly 2-propenoic acid, but, in addition, a small amount of a side product B. The spectral data for this product are shown below in the sequence : 1. 1H NMR , 2. 13C NMR , 3. Mass , 4. IR.

1. NaOH 2. HBr, H2O

+ B (unknown)

OH

O

Br

OH

O A 2-Propenoic acid a. After consideration of the spectral data, write the structure of the product in the box below.

Chemistry 3B, Examination 2 Page 9 1. 1H NMR Spectrum (for expanded section, see bottom spectrum).

Chemistry 3B, Examination 2 Page 10 b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, and C giving rise to the corresponding signals in the spectrum. Use the Table below, if necessary.

Chemistry 3B, Examination 2 Page 11 2. 13C NMR Spectrum.

Draw again your suggestion for the unknown in the box below and label the types of carbon atoms A–C giving rise to the corresponding signals in the spectrum. Hint: The carbon giving rise to the signal labeled B above is attached to the hydrogens giving rise to signal B in the 1H NMR spectrum. Similarly, the carbon giving rise to the signal labeled C above is attached to the hydrogens giving rise to signal C in the 1H NMR spectrum.

Chemistry 3B, Examination 2 Page 12 3. Mass spectrum. Hint: Atomic weights: C = 12; H = 1; O = 16; Br exists in nature as a 1:1 mixture of Br = 79 and Br = 81.

a. Clearly mark on the spectrum the molecular ion(s) as “M+”. b. In the boxes above the respective fragment ions, indicate the molecular piece that has fragmented from M+, e.g. “Cl”, or “CH3O”, or “CH3CH2”, or ?

Chemistry 3B, Examination 2 Page 13 4. IR Spectrum. Confirm or rule out the presence or absence (circle one) of the following bonds. Enter an approximate expected stretching frequency in the box. ν~ (Csp


cm–1 ν~ (Csp


cm–1 ν~ (O–H) is: present absent at

cm–1


cm–1

Chemistry 3B, Examination 2 Page 14 IV. [45 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have!

a. O O

Catalytic H+

Work from left to right in the following spaces. There is more space than you will need.


OH

OH

O

O

H+

+ H2O O

O

O


Chemistry 3B, Examination 2 Page 16 c.

O

O

NaOH, H2O, Δ

O

O H

O

(Don’t worry about stereo-chemistry).

Work from left to right in the following spaces. Hint: Work backwards to unravel the product!

Chemistry 3B, Examination 2 Page 17 V. [45 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms!

N

O

H

a.

+ any other material


Chemistry 3B, Examination 2 Page 18 b. Synthesize (racemic) compound A from 2-butanone and any materials containing four carbons or less.

O

O

O

O

A Work from left to right in the following spaces. There is more space than you will need.

Chemistry 3B, Examination 2 Page 19

c. One step in this sequence will not work. Circle the reaction arrow denoting this step. Note: Appropriate aqueous work-up (when required) follows each step and is not indicated.

OH

COOCH3

H+ cat.O

OLiAlH4 OH

OH

MnO2

OHO

CrO3, H2OCOOH

OH2, Pd

COOH

O

OO

(CH3CH2)2CuLi NaOH, H2O, Δ O

VI. [35 Points] Place an X mark in the box next to the most accurate statement.

a. The reactivity of 1–4 toward NH3 increases in the order

3CCl

O

CH3CNH2

O

CH3COCH3

O

CH3COCCH3

O O

CH 1 2 3 4 1, 2, 3, 4

4, 3, 2, 1

2, 3, 4, 1

3, 2, 1, 4


b. The acidity of 1–4 increases in the order

HCOH

O

CH3COCH3

O

CH3CCH3

O +NH4 1 2 3 4

1, 2, 3, 4

4, 3, 2, 1

2, 3, 4, 1

3, 2, 1, 4 c. A researcher finds two unlabeled bottles containing liquids in a cabinet. He knows that one of them is azacyclohexane A, the other is the ether analog B. A 13C NMR spectrum of the contents of bottle 1 shows δ = 25.5, 27.2, and 47.5 ppm, while that of bottle 2 shows δ = 23.6, 26.6, and 68.0 ppm. What is in bottle 1, A or B? Bottle 1 contains

NH

A

O

Bottle 1 contains

B

Chemistry 3B, Examination 2 Page

21

d. In problem c., give one (and only one) other spectral technique that would solve it and why or how. Place your respective answers into the boxes below. Other spectral technique How will this technique distinguish between A and B? (One sentence or expression only!)

"A little knowledge is a dangerous thing. But, then, so is a lot." A. Einstein

“The End”



Laboratory GSI (if applicable): Peter Vollhardt ______________________ November 4, 2008 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 20 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (25)

II. ______ (50)

III. ______ (50)

IV. ______ (45)

V. ______ (45)

VI. ______ (35)

Total:

(250)

Chemistry 3B, Examination 2 Page 2 I. [25 Points] Write the organic products of the following reactions of the starting amide.

H2SO4, H2O

(LDA) 1.

2. H+, H2O work-up

1. LiAlH4

2. H+, H2O work-up Cl2, NaOH

NH2

O

N Li::AlH

Chemistry 3B, Examination 2 Page 3 II. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is

assumed to follow each step. It is not part of any answer. a. D2O, NaOD

O

Mass spectrum of product: m/z = 102

b.

1. HCN 2. H+, H2O, Δ

H

O

13C Spectrum of product:

Chemistry 3B, Examination 2 Page 4 c. OO d.

CH3COOH

O

O

e.

NaOH, H2O, Δ

H3CCH3

O

O

C6H8O

Chemistry 3B, Examination 2 Page 5 f.

C

O

Cl

COOH g.

Cl

O

CH3

O

h.

OCH3

O

MgBr

2 equiv.

Chemistry 3B, Examination 2 Page 6 i. HCl, CH3CH2OH (solvent) + Product after basic work-up

O

N

O

Two additional neutral reagents j.

O H3C H

NCH3

HTwo reagents

Chemistry 3B, Examination 2 Page 7 III. [50 Points] In an attempt to hydrolyze lactone A with concentrated aqueous HBr, a student obtained compound B. The complete spectral data for this product are shown below in the sequence: 1. 1H NMR, 2. 13C NMR, 3. Mass, 4. IR.

HBr, H2O

B (unknown)

O

O

A a. After consideration of the spectral data, write the structure of the product in the box below.

Chemistry 3B, Examination 2 Page 8 1. 1H NMR spectrum (for expanded section, see bottom spectrum).

B C

D A

ppm

B C D

ppm

Chemistry 3B, Examination 2 Page 9 b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, C,

and D giving rise to the corresponding signals in the spectrum. Use the Table below, if necessary.

Chemistry 3B, Examination 2 Page 10 2. 13C NMR spectrum. B

A

ppm

Draw again your suggestion for the unknown in the box below and label the types of carbon atoms A and B giving rise to the corresponding signals in the spectrum.

Chemistry 3B, Examination 2 Page 11 3. Mass spectrum. Hint: Atomic weights: C = 12; H = 1; O = 16; Br exists in nature as a 1:1 mixture of Br = 79 and Br = 81.

a. Clearly mark on the spectrum the molecular ion(s) as “M+”. b. In the boxes above the respective fragment ions, indicate the structure of the fragment.

Chemistry 3B, Examination 2 Page 12 4. IR spectrum.



cm–1


cm–1

cm–1


Chemistry 3B, Examination 2 Page 13 IV. [45 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have!

a. O O

Catalytic HO−



CH3CNH+, H2O

NH2

O


Chemistry 3B, Examination 2 Page 15 c.

HO−, H2O

H

O HHO

O Work from left to right in the following spaces.

Chemistry 3B, Examination 2 Page 16 V. [45 Points] Provide a reasonable synthetic route from starting material to product.

Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. You need to apply retrosynthesis!

N

O

H

a.

+ any other material



O

H

CN

HOOH


Chemistry 3B, Examination 2 Page 18 c. Synthesize ketone A from starting materials containing one or two carbons only.

O

A Work from left to right in the following spaces. There is more space than you will need.

Chemistry 3B, Examination 2 Page 19 VI. [35 Points] Place an X mark in the box next to the most accurate statement.

a. The reactivity of 1–4 toward H2O increases in the order

3CCl

O

CH3CNH2

O

CH3COCH3

O

CH3COCCH3

O O

CH 1 2 3 4 1, 2, 3, 4

4, 3, 2, 1

2, 3, 4, 1

3, 2, 1, 4 b. The acidity of 1–4 increases in the order

HCOH

O

CH3COCH3

O

CH3CCH3

O CH3NH3

+

1 2 3 4

1, 2, 3, 4

4, 3, 2, 1

2, 3, 4, 1

3, 2, 1, 4


20

c. Explain the following finding in one sentence. For the equilibria shown below, K1 = ~1, but K2 > 1

OH

O+ CH3OH

H+

OCH3

O+ H2O

HO OH

O

H+

O

O

+ H2O

K1

K2

Place your answer into the box below.

“The End”



GSI (if you are taking Chem 3BL): ______________________ Peter Vollhardt November 5, 2009 Please provide the following information if applicable. Making up an I Grade _____ If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 13 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. (30)

II. (30)

III. (50)

IV. (60)

V. (60)

VI. (20)

Total:

(250)

Chemistry 3B, Examination 2 Page 2 I. [30 Points] Name or draw, as appropriate, the following molecules according to the

IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S). a.

Cl

COOH

Br

b.

c. (R)-trans-3-Penten-2-amine

d. 3-Methyl- N-bromo-N-ethylbutanamide

e.

Chemistry 3B, Examination 2 Page 3 II. [30 Points] Write the organic products of the following reactions of the starting acyl bromide.

Br2, HBr

NH3 1.

2. H+, H2O work-up

1. (CH3)2CuLi 2. H+, H2O work-up CH3COOH

OAl

O

H

OLi+

Chemistry 3B, Examination 2 Page 4 III. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is

assumed to follow each step. It is not part of any answer. a. (CH3)2NH, NaBH3CN

O

b. 1. LDA

2. CH3I 3. LiAlH4

c. OO d.

Chemistry 3B, Examination 2 Page 5 e.

1. 2.

“One pot reaction”

CH3

O

f.

C

O

Cl

COOH g. 1. PCC 2. H+, H2O 3. NaOH, H2O, Δ C10H14O h.

MgBr

2 equiv.

C5H10O2

Chemistry 3B, Examination 2 Page 6 i.

1. 2.

j.

Chemistry 3B, Examination 2 Page 7 IV. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! a.

OCH3

ONa+-OCH2CH3, CH3CH2OH

OCH2CH3

O



c. The following atom-economical reaction occurs in a dry solvent (this means: no water!). Although it is new to you, you can apply the principles that you have learned to write a mechanism.



Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. You need to apply retrosynthesis!

a.


Chemistry 3B, Examination 2 Page 12 c. Synthesize compound A from benzene.



13

VI. [20 Points] Place an X mark in the box next to the most accurate statement. a. The reactivity of 1–4 toward NH3 increases in the order

3CCl

O

CH3COCH3

O

1 2 3 4

CH

1, 2, 3, 4

4, 3, 2, 1 2, 3, 4, 1

3, 2, 1, 4

b. The acidity of 1–4 (above) increases in the order

1, 2, 3, 4

4, 3, 2, 1 2, 3, 4, 1

3, 2, 1, 4

c. Circle the most likely product of the following reaction:

Br

“The End”

OBr2,

excess −OH OOor

Br

O OHor or

1

FINAL EXAMINATION Chemistry 3B

Name:__________________________ SID #:______________________ Print first name before second! Use capital letters! Peter Vollhardt May 17, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 25 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Grades will be posted on May 25, by 5 pm, outside 320 Latimer Hall. Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (60)

II. ______ (175)

III. ______ (60)

IV. ______ (40)

V. ______ (60)

VI. ______ (60)

VII. ______ (45)

Total:

(500)

2

I. [60 Points] Provide the IUPAC name or draw the structure, as appropriate, of the following

molecules. Remember the priority of functional groups in choosing names, indicate the correct stereochemistry (e.g., R, S, and E, Z), and do not forget about the alphabetical ordering of substituents!

(a)

COOH

H2N H

(b)

Methyl cis-4-bromocyclohexanecarboxylate

(c)

S

H

3

(d)

N CCH2COCH2CH3

O

(e) (4R)-Bromo-N-ethyl-N-methylpentanamide

(f) COOH

H2N H

CH2CH2SCH3

(This is the amino acid methionine)

4

II. [175 Points; (a) - (j) 10 points each, (k) - (o) 15 points each] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer.

(a)

OS

CH3

OO

CH3OH

-CH3SO3H

(b) 1.

2.

+NH3

COO-C

O

H

(c) hν

13C NMR: δ = 23.4, 32.9, 137.2 ppm

CH3

CH3

5

(d) H+, H2O

O

O 1H NMR: δ = 6.20 (s, 2H), 2.01 (s, 6H) ppm (e)

(f)

H+, CH3OH

(g) CH3NH2, Na+ NCBH3

–

CH3O OCH3

O

CI

CH3 CH3

6

(h) +

O (i) (CH3)2NH

HOOCN

CH3

O

CH3

13C NMR spectrum of starting material: Mass spectrum of starting material:

(j) Na+–OH, H2O +

O O

7

(k) 1. 2. CN 3.

NO2

(l) 1. 2. O 3.

O

(m) 1. PBr3

2. NaCN 3. MgBr

4. H+, H2O OH

8

(n) 1. LiAlH4

2. CH3I (2 equiv) 3. Ag2O

NH

O

m/z = 99 (o)

OCH3

O O

+

NH

OCH3CH3O

H3C CH3

O O +

9

III. [60 Points] Treatment of chloroacetic acid A with methoxybenzene B and AlCl3 led to unknown C. The mass, IR, and NMR spectra of this product are shown in the following pages. AlCl3 ClCH2COOH + C (Unknown)

OC 3H

A B

(a) After consideration of the spectral data, write the structure of the product in the box below. Structure of unknown

b. Interpret the spectral data as requested in the spaces provided, starting on the following page.

10

1. Mass Spectrum Label the molecular ion as “M+” and the base peak as “BP”. Using the partial periodic table on the previous page for atomic weights, draw the structures of the fragment ions at m/z = 148, 135, and 121, respectively, in the boxes below. Draw a “+” charge at the point of the dangling valence in your line structure. m/z = 148 m/z = 135 m/z = 121

11

2. IR Spectrum



cm–1 ν~ (Csp


cm–1


cm–1


cm–1

12

3. 13C NMR Spectrum (scale in ppm). Draw your suggestion for the unknown in the box below and label the types of carbon atoms A, B, C, and D, giving rise to the corresponding signals in the spectrum. Note that B is a group of four signals, which belong to a group of similar carbon atoms, all of which should be labeled “B”.

13

4. 1H NMR Spectrum (scale in ppm; for expanded sections, see below and the next page).

As indicated on the spectrum above, the signal due to proton A disappears in D2O solvent (“exchanges”).

14

Draw your suggestion for the unknown in the box and label the hydrogens A–E giving rise to the corresponding signals in the spectrum. Note: For the assignment of B and C, consider the effect of close lying substituents.

15

IV. [40 Points] You are asked to assign the structures of the two pentoses D-arabinose and D-xylose. Ruff degradation of the former gives D-erythrose, that of the latter D-threose. Kiliani-Fischer extension of D-arabinose furnishes D-glucose and D-mannose, that of D-xylose results in D-gulose and D-idose. CHO CHO

HO H

CH2OH

H OH

H OH

CH2OH

H OH

D-(-)-Erythrose D-(-)-Threose D-Arabinose D-Xylose CHO

OHH

HHO

OHH

OHH

CH2OH

CHO

HHO

HHO

OHH

OHH

CH2OH

CHO

OHH

OHH

HHO

OHH

CH2OH

CHO

HHO

OHH

HHO

OHH

CH2OH

D-(+)-Glucose D-(+)-Mannose D-(-)-Gulose D-(-)-Idose 1. Draw your assignments in the respective boxes, using Fischer projections.

16

2. Specify the conditions of (a) the Ruff degradation

1. 2.

(b) the Kiliani-Fischer extension

1. 2.

17

V. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need. (a) OH

BrBr

Br

NaOH, Br2

O

18

(b) 1. LiAlH4 2. H+, H2O, Δ

OH

H


need.

19

(c) H+, CH3CH2OH + CH2=O + CH3NH2

H

CH3

N

H3C

O

H

H

O


20

VI. [60 Points] Provide a reasonable synthetic route from starting materials to product. Note: Several steps are required, and there may be more than one solution to the problem. You may use any additional organic or organometallic reagents to effect your conversions. Do not write mechanisms!

Br

Br(a)


21

(b)

H2NCHCOOH and H2NCH2COOH

CH(CH3)2

2NCHCNHCH2COOH

CH(CH3)2

O

H

Valine Glycine

Val-Gly 1. Protection of valine

2. Protection of glycine

3. Dipeptide formation

22

(c)

O

O O


23

VII. [45 Points] Place an X mark in the box next to the most accurate statement.

(a) The longest wavelength band in the UV spectra of the hydrocarbons below moves to lower energy in the order

1 2 3 1, 2, 3

3, 2, 1

2, 3, 1

3, 1, 2

(b) Circle the compounds which are aromatic

N O+O

24

(c) The pKa values of the following compounds decrease in the order

O

CH3OH

N

H

+ N

H

1 2 3 4

1, 2, 3, 4

4, 3, 2, 1

2, 3, 4, 1

3, 4, 2, 1 (d) The rates of electrophilic aromatic nitration of the following compounds increases in the order

NO2

Cl

Cl

NO2

S

1 2 3

1, 2, 3

2, 1, 3,

3, 2, 1

2, 3, 1

25

(e) Oxidation of idose to idaric acid causes

CHO

HHO

OHH

HHO

OHH

CH2OH

COOH

HHO

OHH

HHO

OHH

COOH

HNO3 Idose Idaric acid the specific rotation to go to zero the 13C NMR spectrum to simplify to 3 lines the sugar to become reducing mutarotation

The End Have a great summer!


1



Laboratory GSI (if applicable): Peter Vollhardt ______________________ December 15, 2006 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 25 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Grades will be posted on Wednesday, December 20, by 5 pm, outside 320 Latimer Hall. Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (60)

II. ______ (175)

III. ______ (60)

IV. ______ (40)

V. ______ (60)

VI. ______ (60)

VII. ______ (45)

Total:

(500)

2


molecules. Remember the priority of functional groups in choosing names, indicate the correct stereochemistry (e.g., R, S, and E, Z), and do not forget about the alphabetical ordering of substituents!

(a)

(2S)-Amino-6-heptynoic acid

(b)

ClCl

Br

(c)

(R)-2, 3-Dihydroxypropanal

3

(d)

OCH2CH3

OO

(e)

N-(2-Methylpropyl)ethanamide

(f)

O

4


(a)

OS

CH3

OO

Na+-OCH3, CH3OH

(b) 1.

2.

NH2

O

OCH3

CH3 CH3O

OCH3

H

H(c)

5

(d)

P2S5

O

O

1H NMR: δ =2.35 (s, 6H), 2.01 (s, 6H) ppm (e)

N

CH3

HNO3, H+

(f)

O

H

HO

H

HO

HO

H

HHOH

OH

CH3OH, H+

(g)

O

CH3NH2, Na+ NCBH3–

6

(h) +

CN

(i) 13C NMR δ = 220.2, 38.3, 23.3 ppm (j) Na+–OCH3, HCH3OH

1H NMR spectrum:

CH3COOH

O

O

O

OCH3

O O

7

(k) 1.

NH

O 2. 3.

+N N

(l) 1. 2. 3COCH3

O

CH3CHCH2COCH3

OH O

CH

(m) 1. CH3OH, H+

2. 2 CH3MgBr

H+, CH3OH

OH

O

8

(n) 1. NaCN

2. CH3CH2CH2MgBr 3. CH2=P(C6H5)3

CH3I Mass spectrum of product: (o)

OCH3

O O

+

NH

OCH3CH3O

H3C CH3

O O +

9

III. [60 Points] In an attempt to effect electrophilic methoxylation, benzene carbaldehyde A was treated with methyl hydroperoxide B in the presence of acid. The mass, IR, and NMR spectra of this product are shown in the following pages. From the complex mixture of products, traces of unknown C were obtained. H+

C (Unknown) + CH3OOH

H

O

A B

(a) After consideration of the spectral data, write the structure of the product in the box below. Structure of unknown

b. Interpret the spectral data as requested in the spaces provided, starting on the following page.

10


11

b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, C, and D giving rise to the corresponding signals in the spectrum. Use the Table below, if necessary. 2. 13C NMR Spectrum.

12

Draw again your suggestion for the unknown in the box below and label the types of carbon atoms A–E giving rise to the corresponding signals in the spectrum. 3. Mass spectrum.

13

a. Clearly mark on the spectrum the molecular ion as “M+”. b. In the boxes above the respective fragment ions, indicate the molecular piece that has fragmented from M+, e.g. “Cl”, or “CH3O”, or “CH3CH2”, or ? 4. IR Spectrum.

14



ν~ (Csp


ν~ (O–H) is: present absent at cm–1


cm–1

15

IV. [40 Points] You are asked to assign the structures of the two pentoses D-ribose and D-lyxose. Ruff degradation of the former gives D-erythrose, that of the latter D-threose. Kiliani-Fischer extension of D-ribose furnishes D-allose and D-altrose, that of D-lyxose results in D-galactose and D-talose ribose. CHO CHO

HO H

CH2OH

H OH

H OH

CH2OH

H OH

D-(-)-Erythrose D-(-)-Threose D-Ribose D-Lyxose CHO

OHH

OHH

OHH

OHH

CH2OH

CHO

HHO

OHH

OHH

OHH

CH2OH

CHO

OHH

HHO

HHO

OHH

CH2OH

CHO

HHO

HHO

HHO

OHH

CH2OH

D-Allose D-Altrose D-Galactose D-Talose 1. Draw your assignments in the respective boxes, using Fischer projections.

16

2. Specify the conditions of (a) the Ruff degradation

1. 2.

(b) the Kiliani-Fischer extension

1. 2.

17

V. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need. (a)

NaOH, Δ

OH

OH

O

18

(b) 1. LiAlD4 2. H+, H2O (work up)

O

ON

CH3

N

O

OH

CH3

CH2D


need.

19

(c) NaBH3CN, CH3OH 2N

H

O

NH

H


20

VI. [60 Points] Provide a reasonable synthetic route from starting materials to product. Note: Several steps are required, and there may be more than one solution to the problem. You may use any additional organic or organometallic reagents to effect your conversions. Do not write mechanisms!

(a)

N O

O

H


21

(b) H2N CNH

O

COOH

H2N COOH

22

(c) The only organic starting materials:

OCH3

O O OCH3

N NO

O

O


23


(a) The longest wavelength band in the UV spectra of the hydrocarbons below moves to lower energy in the order

1 2 3 1, 2, 3

3, 2, 1

2, 1, 3

3, 1, 2

(b) Circle the compounds which are aromatic

O2N H

+N

N

O

N

NH

O

O

24

(c) In the collection below, circle the most abundant fragments formed during the mass spectral ionization of 2-pentanone.

O

70 eV H+ C O CH3+ CH3CH

2

+ CH 2

+3CH2CH C3H6O+ C2H4

+

(d) The rates of electrophilic aromatic nitration of the following compounds increases in the order

Cl

Cl

N NCH3

1 2 3

1, 2, 3

2, 1, 3,

3, 2, 1

2, 3, 1

25

(e) Give the products and their molar amounts per mole of starting material of the complete periodic acid oxidation of D-erythrose and D-erythrulose.

CHO

OHH

OHH

CH2OH

HIO4 D-Erythrose

CH2OH

O

OHH

CH2OH

D-Erythrulose

The End

Merry Christmas!


1



Laboratory GSI (if applicable): Peter Vollhardt ______________________ December 17, 2008 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 25 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (60)

II. ______ (175)

III. ______ (60)

IV. ______ (40)

V. ______ (60)

VI. ______ (60)

VII. ______ (45)

Total:

(500)

2


molecules. Remember the priority of functional groups in choosing names and indicate the correct stereochemistry (cis, trans, E, Z, R, and S, as appropriate)!

(a) Trans-3-oxo-4-hexenal

(b) 1-Bromo-4-(2,2-dichloropropyl)benzene

(c) (R)-2,3-Dihydroxypropanenitrile

1

2

3

(Fischer projection)

The numbers refer to the main chain

3

(d)

OCH2CH3

OH2N H

(e) N-Chloro-N-methyl-3-pentanamine

(f)

O

4


(a)

OS

CH3

OO

+CH3OH

O

O

O

O

Na+

(b) 1.

2.

NH2

H3CO

OCH3

H3CO

CH3O

OCH3

H3CO I

(c)

H

H

5

(d)

O

O

NH3, H+

13C NMR spectrum:

(e)

H3CN

HNO3, H+

NH2 (f)

O

H

H3CO

H

H3CO

H3CO

H

HHOCH3

OCH3

H2O, H+

mildly acidic O

6

(g) Two reagents

NH CH3

O

(h)

+

CN

H3CO

CN

(i) + NaOH

H2N ONH2

7

(j) OH

H3CO

1. LiAlH4 2. H+, H2O

IR spectrum of starting material:

13C NMR spectrum of starting material:

8

(k) 1. 2.

H3C OH O (l) 1. 2. 3.

OH

NH2

NH2

Br

(m) HIO4

2 HCOOH + 1 CH2=O An aldose

9

(n) 2.

CH3

1. N Br

O

O

Mass spectrum of product: 1H NMR spectrum of product:

ppm (o) 1. MnO2 2. NH3 + 3.

COOH

NH2

OH

10

III. [60 Points] Diethyl malonate A was treated with bromine to give a product B. The mass, IR, and NMR spectra of B are shown in the following pages in the sequence :

1. 1H NMR , 2. 13C NMR , 3. Mass , 4. IR. B

Br2

OO

OO

A

(a) After consideration of the spectral data, write the structure of B in the box below. Structure of B

11

1. 1H NMR spectrum (for expanded sections, see bottom spectra).

ppm

A

B

C

C (B

A

J = 8 Hz) (J = 8 Hz)

ppm ppm

12

b. Draw again your suggestion for B in the box and label the hydrogens A, B, and C giving rise to the corresponding signals in the 1H NMR spectrum. Use the Table below, if necessary.

13

2. 13C NMR spectrum.

A

B

C

D

14

Draw again your suggestion for B in the box below and label the types of carbon atoms A–D giving rise to the corresponding signals in the spectrum. 3. Mass spectrum. Hint: Atomic weights: C = 12; H = 1; O = 16; Br exists in nature as a 1:1 mixture of Br = 79 and Br = 81.

a. Clearly mark on the spectrum the molecular ion(s) “M+”. b. In the boxes below, indicate the structure of the fragment ions with the m/z value given under the box. m/z = 193/195 29

15

4. IR Spectrum.



ν~ (Csp



cm–1


cm–1

16

IV. [40 Points] (a) D-Ribulose is a non-reducing pentose. Treatment with NaBH4 gives two alditols. One of them is identical to the product of NaBH4 reduction of D-ribose, the other is identical to the product of NaBH4 reduction of D-arabinose. Fill in the blanks below and provide a structure for D-ribulose. NaBH4

An alditol An alditol D-Ribulose NaBH4 NaBH4 CHO

HHO

OHH

OHH

CH2OHD-Arabinose

OHH

OHH

OHH

CH2OH

CHO

D-Ribose

(b) D-Erythrose was treated with aqueous bromine to give the aldonic acid A, which was

subsequently thermally dehydrated to B, and then treated with acidic acetone to give the final product C. Provide structures for A and B. CHO

H OH

CH2OH

H OH

Br2, H2O Δ

−H2O

−H2O

OH

OH

C

CH2

O

OCH3

CH3Note: These"corners" are not atoms.

D-Erythrose A B

C

H+, H3C CH3

O

17

V. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need. (a)

CH3

O

NaOH, H2O, Δ

H3C

O

+

O

CH3

18

(b)

NO2

O2N

O

2 NaOH, H2O NO2

O2N

Br

O

O


19

(c)

OH

CH3

CH3

H+, H2O

O

H3C CH3 Work from left to right in the following spaces. There is much more space than you will

need.

20

VI. [60 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. You need to apply retrosynthesis! You may use any additional organic or organometallic reagents to effect your conversions.

(a)

NH2

Note:

HCCl,

O

HCCl,

NH

H2NCCl,

O

and ClCH2NH2 do not exist and are not allowed as reagents.


21

(b)

H2N

O

COOH

NHNH2

COOH

22

(c) For this problem, use the materials given below as the only organic compounds:

IO

O I

O

Starting material

Additional organic reagents


23

VII. [45 Points] Place an X mark in the box next to the most accurate statement. (a) The acidity of 1–4 increases in the order

H3NCH2COH

O CH3NH3 CH3C N H

1 2 3 4

1, 2, 3, 4

4, 3, 2, 1

4, 1, 2, 3

3, 2, 1, 4

(b) In the 1H NMR spectrum of the compund below circle the hydrogens that you expect to show peaks in the “left half” of the spectrum (that is δ > 5 ppm).

N

NO

OH

H

O

O

H

Cl

H H

H

H

24

(c) The following Diels-Alder reaction follows the endo rule. True or false? Circle the correct answer below

CH3

CO2CH3

CO2CH3

+CO2CH3

CO2CH3

CH3

H

H

True False (d) The mass spectrum of N,N-dipropylpropanamine (see below) shows only a relatively small molecular ion peak at m/z = 143. The base (100%) peak is a fragment at m/z = 114. In the box below the spectrum, draw the structure of this fragment (including charges).

N N,N-dipropylpropanamine

25

(e) Aromatic heterocycles are frequently constructed in one step by a combination of aldol and imine condensations. With this statement in mind provide the most suitable retrosynthetic disconnection of A into two starting materials (boxes).

N CH3

CH3

CH3

O

A

+

The End

Merry Christmas!

1



GSI (if you are taking Chem 3BL): ______________________

Peter Vollhardt December 16, 2009 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 19 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______

(60)

II. ______

(175)

III. ______

(60)

IV. ______

(40)

V. ______

(60)

VI. ______

(60)

VII. ______

(45)

Total:

(500)

2

I. [60 Points] Name or draw, as appropriate, the following molecules according to the

IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S). (a) (R)-4-bromo-N-ethyl-N-methyl-pentanamide

(b) 1-Bromo-4-(2,2-dichloropropyl)benzene

(c) (R)-2,3-Dihydroxypropanal

(Fischer projection)

The numbers refer to the main chain

3

(d)

(e) Methyl 3-oxo-butanoate

(f)

4


(a)

H2, Pd–C

C6H8O (b) 1.

2.

NH2

H3CO

OCH3

H3CO

(c)

H

H

5

(d)

(e)

(f)

(g) H CH3 NaBH3CN, CH3OH H2C=O +

N

6

(h)

OCH3

Complete the stencil above (i)

H3C

O

O

(j)

OH

H3CO

7

(k) 1. 2. (l) 1. 2. 3. (m) HIO4

2 HCOOH + 1 CH2=O An aldose

8

(n) (o) 1. MnO2 2. NH4CN 3. H+, H2O, Δ

OH

9

III. [60 Points] The wavy lines in the following structure indicate four possible retrosynthetic disconnections of four bonds (numbered 1-4). O

1 2 3 4

Show the respective four reactions that would lead to the generation of each of these strategic bonds in the four boxes below. Note: It is fine to use a protected or otherwise modified fragment to make the desired connection, as long as it can be elaborated later into the target structure. However, do not show such elaboration. Each box should contain only the reagents that you would use to make the bond in question. Bond 1: Bond 2: Bond 3: Bond 4:

10

IV. [40 Points] (a) D-Ribulose is a pentaketose. Treatment with NaBH4 gives two alditols. One of them is identical to the product of NaBH4 reduction of D-ribose, the other is identical to the product of NaBH4 reduction of D-arabinose. Fill in the blanks below and provide a structure for D-ribulose. NaBH4

D-Ribulose An alditol An alditol NaBH4 NaBH4

CHO

HHO

OHH

OHH

CH2OHD-Arabinose

OHH

OHH

OHH

CH2OH

CHO

D-Ribose

(b) D-Erythrose was treated with nitric acid to give the aldaric acid A, which was treated

with acidic acetone to give B. On heating, B dehydrated to the final product C. Provide structures for A and B.

11

V. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! Work from left to right in the following spaces. There is more space than you will need. (a)

H+, H2O, THF

12

(b) H+, H2O


13

(c) H+, H2O, Δ


14

VI. [60 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. You need to apply retrosynthesis! You may use any additional organic or organometallic reagents to effect your conversions.

(a)


15

(b)

O

NH

S

NH2

S

HOOC


16

(c)


17

VII. [45 Points] Place an X mark in the box next to the most accurate statement. (a) The acidity of 1–4 increases in the order:

H3NCH2COH

O CH3NH3 CH3C N H

1 2 3 4

1, 2, 3, 4

4, 3, 2, 1

1, 4, 2, 3

3, 2, 1, 4

(b) The following two sugars are:

CHO

OHH

HHO

OHH

OHH

CH2OH CHO

HO H

H OH

HO H

HO H

CH2OH

Identical

Enantiomers

Diastereomers

Anomers

18

(c) The following heterocycle will undergo electrophilic bromination at position:

N

N S

1

23

4

1

2

3

4 (d) The following reaction will give

O

O

Na+ −OCH2CH3, CH3CH2OH

O

OO

OH

O

O

OO

19

(e) Which of the following molecules are reduced by LiAlH4? Check all the boxes that apply.

OH

O

N

Cl

The End

Merry Christmas!

1



GSI (if you are taking Chem 3BL): ______________________ Peter Vollhardt September 23, 2010 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 15 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______ (30)

II. ______ (30)

III. ______ (50)

IV. ______ (40)

V. ______ (40)

VI. ______ (40)

VII. ______ (20) Total:

(250)

2

I. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S).

a. (S)-1-(2-Chlorobutyl)-2-nitrobenzene

b. cis-Hexa-1,3-diene

c.

O

CH3

CH3

Pure enantiomer

d.

3

e. 4-Oxopentanal

II. [30 Points] Compound A undergoes preferential electrophilic nitration to give only one product.

CF3

12

3

HNO3, H2SO4or

A

4

OH

5

6

or

CF3

OH

NO2

CF3

OH

CF3

OH

O2N

O2N

a. Which one? Mark the box below your choice with an X, preferably after you have completed questions b.–d. b. Write all the resonance forms of the intermediate formed by attack of NO2

+ on A at:

C-2:

CF3

12

34

OH

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures. Write the nitro group as “NO2” (no need for the Lewis structure).

4

C-5:

CF3

12

34

OH

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures. Write the nitro group as “NO2” (no need for the Lewis structure). C-6:

CF3

12

34

OH

5

6

Note: A first stencil is provided for format. Leave out the numbering in any additional structures. Write the nitro group as “NO2” (no need for the Lewis structure). c. Circle (in your answers above) the most strongly contributing resonance forms of the attack at C-2, C-5, and C-6. d. Considering all of the above most strongly contributing resonance forms, which one is the best overall? Redraw it in the box below.

CF3

12

34

OH

5

6

5


a.

Two isomers. Add the missing pieces. b.

Kinetic product Thermodynamic product Hint: Electrophilic attack occurs preferentially at C-1.

BrH2C Br2

1

23

4

6

c.

CH3

+

CN

CN

O O

Complete the stencil above, showing clearly stereochemistry (hashed and wedged bonds).

d.

hν


e. OH

OH

MnO2

7

f. 1.

2.

g.

F

HO3S

HNO3, H2

CH3

SO4

O2N

h.

O2N

Cl

Br2, FeBr3

Monobromination

8

i. j.

HC

CH3H3C

SO3, H2SO4

HC

H2N

CH3H3C

1.

2.

3. H+, H2O

9

IV. [40 Points]

a. Rank the following arenes in order of reactivity (highest to lowest) toward electrophilic

aromatic substitution. Mark the box next to the best answer below.

Cl

Br

OCH3

CF3

NO2

1 2 3 4

1, 2, 3, 4 3, 1, 2, 4 3, 2, 1, 4 3, 1, 4, 2 b. Among the compounds shown below, circle those that are stabilized by conjugation.

10

c. One of the compounds shown below is aromatic. Circle its structure.

CH3

CH3

d. Rank compounds 1–5 in order of increasing reactivity as dienes in the Diels-Alder reaction:

1, 2, 3, 4, 5 1, 4, 2, 3, 5 3, 1, 5, 4, 2 5, 3, 1, 4, 2 3, 5, 1, 2, 4

11

V. [40 Points] Write detailed stepwise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have!

a.


12

b. Hydrocarbon A is doubly deprotonated by methyllithium to give the aromatic dianion B. Treatment of B with bromine at low temperatures gave C. Write a plausible mechanism that leads from B to C.


13


a.


need.

14

b. Synthesize compound A from any acyclic materials and any other reagent. Hint: Think Diels-Alder reaction. Caution: Work backwards. CO2CH3

O

A (racemate) Work from left to right in the following spaces. There is much more space than you will need.

15

VII. [20 Points] Place an X mark in the box next to the most accurate statement. a. The Diels-Alder reaction is made possible because a racemate is formed

the (4N+2) rule overrides the Lewis octet rule

of two isomeric products the less stable one is formed

the reaction requires heat to go to completion

an aromatic transition state b. The bromine substituent in bromobenzene directs electrophiles ortho/para because it is inductively donating it is inductively electron-withdrawing

it stabilizes the cationic intermediates by resonance

it is sterically hindered

it is an electron acceptor by resonance

♫ The End ♫



GSI (if you are taking Chem 3BL): ______________________ Peter Vollhardt October 28, 2010 Please provide the following information if applicable. Making up an I Grade _____ If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 13 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. (30)

II. (30)

III. (50)

IV. (60)

V. (60)

VI. (20)

Total:

(250)

Chemistry 3B, Examination 2 Page 2 I. [30 Points] Name or draw, as appropriate, the following molecules according to the

IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S). a.

HO H

O

O

b. N-Methylpent-2-ynamide

c.

H2N

COOH

d.

O O

Br

e. (Z)-4-Hydroxybut-2-enal

Chemistry 3B, Examination 2 Page 3 II. [30 Points] Write the organic products of the following reactions of the starting ester. Neutralizing aqueous work up is assumed.

(CH3)2NH, 250 °C

LiAlH4

CH3MgBr (2 equiv) NaOH, H2O

N Li+1.

2. O

Molecular formula = C5H8O2

Chemistry 3B, Examination 2 Page 4 III. [50 Points] Add the missing components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is

assumed to follow each step. It is not part of any answer. a. CH3CH2OH, CH3CH2O–Na+

b. 1. LDA

2. CH3I 3. LiAlH4

c. 2 d.

Chemistry 3B, Examination 2 Page 5 e.

O

O

OBr

+

Br

OO

OH

f. PCl5 g. 1. 2. h.

MgBr CH3CN

Chemistry 3B, Examination 2 Page 6 i.

j. NaCNBH3, CH3OH

Chemistry 3B, Examination 2 Page 7 IV. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! a.

O

Ocatalytic H2SO4,

THFHO OH

OO



c.



Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. Apply retrosynthesis! It will help you obtain at least partial credit.

a. You may use any additional simple reagents.

and

as starting materials

NHCH3


Chemistry 3B, Examination 2 Page 12 c. Synthesize compound A from benzene.



13

VI. [20 Points] Place an X mark in the box next to the most accurate statement. a. The equilibrium constant K for the hydration of 1–4 increases in the order

1, 2, 3, 4

4, 3, 2, 1 2, 3, 4, 1

2, 3, 1, 4

b. The basicity of 1–4 increases in the order

1, 2, 3, 4

4, 3, 2, 1 2, 1, 4, 3

3, 2, 1, 4

They failed

Chem 3B….

“The End”

1



GSI (if you are taking Chem 3BL): ______________________

Peter Vollhardt December 15, 2010 Please provide the following information if applicable. Making up an I Grade _____ (If you are, please indicate the semester during which you took previous Chem 3B: ––––––––––––––– –––––––––––– Semester Instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 19 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE

I. ______

(60)

II. ______

(175)

III. ______

(60)

IV. ______

(40)

V. ______

(60)

VI. ______

(60)

VII. ______

(45)

Total:

(500)

2

I. [60 Points] Name or draw, as appropriate, the following molecules according to the

IUPAC rules. Indicate stereochemistry where necessary (cis, trans, E, Z, R, or S). (a)

O

NH

(b) 2-Chloro-1-methyl-4-(2-propenyl)benzene

(c)

3

(d)

(e) 4-Fluoro-2-iodopyrrole

(f) N-Ethyl-3-methylpent-4-ene-1-amine

4

II. [175 Points; (a)–(j) 10 points each, (k)–(o) 15 points each] Add the missing

components (starting materials, reagents, or products) of the following reactions in the boxes provided. Aqueous work-up (when required) is assumed to be part of a step. It is not part of any answer.

(a)

Cl

O

OCH3

Cl2

(b) 1.

2.

OCH3

NH2

(c) Δ

5

5

(d)

O

OO

ONH2

1.

2. O

OH

H2N

(e)

(f)

6

(g) H2C=O + NH3 +

NH

CNNC

(h)

(i)

OCH3O

O

Na+–OCH3, CH3OH, Δ

(j) 1. Li

2.

7

(k)

MgBr

H

OH

(l) 1. 2. 3.

OH

4. Δ (m)

1 HCOOH + 2 CH2=O + 1 CO2

HIO4

A D-ketose

8

(n) C6H13N (o) 1. MnO2 2. +NH4

–CN 3. H+, H2O, Δ

9

III. [60 Points] The wavy lines in the following structure indicate four possible retrosynthetic disconnections of four bonds (numbered 1-4).

N

O

12 3 4

Show the respective four reactions that would lead to the generation of each of these strategic bonds in the four boxes below. Note: It is fine to use a protected or otherwise modified fragment to make the desired connection, as long as it can be elaborated later into the target structure. However, do not show such elaboration. Each box should contain only the reagents that you would use to make the bond in question. Bond 1: Bond 2: Bond 3: Bond 4:

10

IV. [40 Points] In water, ribose exists mainly in its cyclic furanose form (both structures are shown below). A researcher finds a bottle of “ribose monomethyl ether” and wants to know the position of the methoxy group. There are five options, indicated by boxes in the two structures given for ribose. NaBH4 reduction of “ribose monomethyl ether” gave an optically active compound A. HNO3 produced optically active dicarboxylic acid B. Ruff degradation of “ribose monomethyl ether”, followed by NaBH4 reduction led to optically active compound C. Fill in the blank boxes below with the structures of A, B, C, and “ribose monomethyl ether”.

A A

NaBH4

Ribmono

et

osemethylher

1. Ruff

degradation2. NaBH4

B C

11

V. [60 Points] Write detailed step-wise mechanisms for the following transformations. Use only structures and “arrow-pushing” techniques. Note: These are not synthetic problems. Do not add any reagents! What you see is what you have! (a)


12

(b)


13

(c)

Hint: There is no water.


14

VI. [60 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required, and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. Apply retrosynthesis! It will help you obtain at least partial credit.

(a)


15

(b)


16

(c)

You may use additional organic or organometallic reagents containing seven carbons or less to effect your conversions. Work from left to right in the following spaces. There is much more space than you will need.

17


(a) The product of the following Diels-Alder reaction is

+OCH3

O

O

OCH3

endo

exo

entropically favored

kinetically disfavored

(b) Show by an arrow the most likely site of protonation of the following molecule:

N

N NH

NH2

O

H2N

18

(c) In the following molecule, circle all possible sites of reduction by excess LiAlH4:

HN

O

H

OCH3

CN

OO

O

(d) The following scheme describes part of an industrial synthesis of the drug Chantix. One step will not work. Circle which one.

1. O32. H2, Pt

CHO

CHO

C6H5CH2NH2,H+, H2, Pt NCH2C6H5

H+, H2O

NHCF3COCCF3

O O

NCCF3

OHNO3, H+

NCCF3

OO2N

O2N

19

(e) Circle the most thermodynamically stable of the following isomers:

OO

O

H

O

OH

The End

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