examination 1 chemistry 3b name: sid
TRANSCRIPT
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.
A cyclobutene
H3C
H3C
CH3
OCH3
5
c.
+
CN
CN
d.
h
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,
i. 1. P(C6H5)3
2. CH3Li 3.
O
I
7
j. H2NNH2, , 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+,
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. ~ (Csp
2�–H) is: present absent at
cm-1
9
~ (O�–H) is: present absent at
cm-1
~ (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
Work from left to right in the following spaces. There is much more space than you will need.
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
EXAMINATION 1 Chemistry 3B
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.
h
C(CH3)3
C(CH3)3
5
c.
+ O
O
O
d.
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.
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
Confirm or rule out the presence or absence (circle one) of the following bonds. Enter an approximate expected stretching frequency in the box. ~ (Csp
2�–H) is: present absent at cm�–1
~ (Csp�–H) is: present absent at
cm�–1 ~ (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 max 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
Work from left to right in the following spaces. There is much more space than you will need.
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
1
EXAMINATION 1 Chemistry 3B
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.
h
CH3
CH3
c.
+ O
O
O
6
d.
CH3
CH3
Product of ring opening
e.
NBr
O
O
h+ 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
1. 1H NMR Spectrum (for expanded section, see bottom spectrum).
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. ~ (Csp
2�–H) is: present absent at cm�–1
~ (Csp
3�–H) is: present absent at
cm�–1 ~ (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 max 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
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! 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.
Work from left to right in the following spaces. There is much more space than you will need.
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