chem 203 final exam december 11, 2008

CHEM 203

Final Exam December 11, 2008

Your name:

This a closed-notes, closed-book exam

You may use your set of molecular models

This exam contains 13 pages

Time: 2h 30 min 1. ________ / 16 2. ________ / 24 3. ________ / 20 4. ________ / 30 5. ________ / 40 6. ________ / 40 7. ________ / 40 8. ________ / 40 TOTAL ________ / 250 = ________ / 100

This exam counts for 45% of your CHEM 203 final grade

Chem 203 final exam p. 2 of 13

1. (16 pts.) Indicate the approximate pKa's for the Bronsted dissociation of the proton in boldface in the following molecules (write your answers in the appropriate boxes)

CH3 O

H

H

H

N

H

H

C

H

HH

H

CH3–CH2–O–HCH3 C C–H

H–Cl

H–F

H OSO3H

2. (24 pts.) Draw: a. Accurate mechanisms for an example of E2 reaction and an example of E1 reaction: E2:


E1: b. Two isomeric alkenes that furnish only compound A upon treatment with O3 followed by Zn / H+ (write your answers in the appropriate boxes):

O

OA

and

c. A carbocation that is stabilized by NO hyperconjugative interactions with C–H bonds, and that will rearrange to form a new carbocation stabilized by eight hyperconjugative interactions with C–H bonds:


d. An alkyl halide that is likely to react with CH3ONa to give a product of substitution, and one that is likely to react with CH3ONa to give a product of elimination:

undergoes substitution undergoes elimination

e. An alkene that produces an achiral diol when treated with OsO4 followed by aqueous NaHSO3, but a chiral diol when treated with MCPBA followed by aqueous H2SO4: f. An achiral molecule that is a meso form, and an achiral molecule that is not a meso form:

achiral and meso achiral, but not meso


3. (20 pts.) Write an accurate mechanism for the following known reactions:

a.

OH

HO

H2SO4

heat O

OCH3

MCPBA

CH3OH

OCH3

OCH3

OH

b.


4. (30 pts.) Check the appropriate box to indicate whether the following procedures represent satisfactory or poor methods for the preparation of the compounds shown:

satisfactory poor

CH3

N3

H

CH3

H1. BH3, then H2O2, aq. NaOH

2. TsCl, pyridine3. NaN3

O

H

HCH3OH

cat. H2SO4 OCH3

H

HHO

CH3 O

SH

1. NaH

2. Mild H3O+

CH3

OH

H H

HH S

OH

1. PCC

2. CH3MgBr,

then mild H3O+

3. Jones reagentO

1. Cl2, h!

2. CH3SNaSCH3

1. Na, NH3 (liq)

2. O3, then

Zn / H+

3. CH3Li, then

mild H3O+

OH

a.

b.

c.

d.

e.

f.


5. (40 pts.) An unknown organic compound, A, was found to be possess appreciable anti- inflammatory activity. As indicated in the scheme below, A was recovered unchanged from a treatment with NaBH4; however, it reacted with LiAlH4 to furnish substance B. Reaction of B with PBr3 and treatment of the resultant with potassium tert-butoxide yielded C, which upon ozonolysis followed by Zn / H+ afforded D as one of the products.

A

NaBH4no reaction

LiAlH4

B

1. PBr3

2.OK

C

O3, then

Zn / H+

D

(one of the products)

then mild

H3O+then mild

H3O+

The spectra of A, B, and D are shown below. Deduce the structures of compounds A, B, C, and D and write your answers in the appropriate boxes.

spectra of A

1H

5H

1H

3H

1702 cm–1

spectra of B

1H

5H

1H

3H

2H

3370 cm–1


spectra of D

3H

3H2H

1690 cm–1

structure of A structure of B

structure of C structure of D


6. (40 pts.) Draw the structure of the major product expected from each of the following reactions. Write your answers in the appropriate boxes. If you should conclude that a given substrate will not react with the reagent(s) shown, write "NO REACTION" in the box.

Important: where appropriate, molecules must be drawn with the correct configuration

H

H

Cl

1.

2. MCPBA

3. NaCN, then

mild H3O+

OKa.

b.

c.

d.

e.

1. CH3MgBr2. D2O

3. H2, Lindlar catalyst

1. HBr2.

3. Na. NH3(liq)

C C–NaCH3

Cl

1. BH3

2. H2O2, aq.

NaOH3. NaH

O1. OsO4

2. aq. NaHSO3

3. cat. H2SO4

60 °C removal of H2O

this product has formula C7H12O2


7. (40 pts.) Indicate all the reagents, catalysts, etc., in the correct order, that are necessary to induce the transformations outlined below. List such reagents above / below the reaction arrows. If a product does not appear to be available from the substrate shown by any method known to you, write "INACCESSIBLE" on the reaction arrow.

N3

OH

SCH3

CH3S

H

H

a.

b.

c.

d.

e.

f.

g.

h.

OH

OCH3

O

OCH3

O

O

OH ONH2

S

H


8. (40 pts.) Propose a good synthesis of the molecules shown below using only methanol, acetylene and ethylene oxide (see below) as the sources of carbon atoms. Intermediates / products obtained during an earlier sequence may be employed in a subsequent procedure, without showing their preparation again. Assume the availability of all necessary reagents (such as bases, acids, KCN, Mg, TsCl, PCC, PBr3, MCPBA, etc.).

CH3OH H–C C–H H2C CH2

O

methanol acetylene ethylene oxide

It is not necessary to write mechanisms

O

O

a.

b. O

CH3


c.

Br

d. OH

O


Characteristic Infrared Absorptions of Common Functional Groups

Functional Group Bond Frequency Range (cm–1) Functional Group Bond Frequency Range (cm–1)

Alcohol O–H 3400 – 3650 (s, broad) Nitrile C N 2210 – 2260 (w – m)

C–O 1050 – 1150 (s) Carboxylic acid O–H 2500-3100 (s, broad) Ether C–O 1000 – 1260 C=O 1700 – 1720 (s) Amine N–H 3300 – 3350 (m) Ester C=O 1710 – 1750 (s) Alkane C–H 2850 – 2950 (m – s) Acyl halide C=O 1770 – 1820 (s) Alkene =C–H 3020 – 3100 (m) Acid anhydride C=O 1740 – 1790 (s)

C=C 1640 – 1680 (m) 1800 – 1850 (s) Alkyne

C H 3270 – 3330 (s) Amide C=O 1630 – 1700 (s)

C C 2100 – 2260 (w – m) Aldehyde, ketone C=O 1680 – 1730 (s)

Characteristic Proton (1H) NMR Chemical Shifts

Type of Hydrogen

Structure Chemical Shift δ (ppm)

Type of Hydrogen

Structure Chemical Shift δ (ppm)

Reference (CH3)4Si 0.00 Amines C HN

2.3 – 3.0

Alkane, primary -CH3 0.7 – 1.3 Alcohol, ether C HO

3.3 – 4.0

Alkane, secondary

-CH2- 1.2 – 1.4 Ester C HOC

O

3.7 – 4.8

Alkane, tertiary C H

1.4 – 1.7 Olefinic C=C-H 5.0 – 6.5

Allylic, primary C=C-CH3 1.6 – 1.9 Aromatic Ar–H 6.5 – 8.0

Methyl carbonyl C CH3

O

2.1 – 2.5 Aldehyde HC

O

9.7 – 10.0

Aromatic methyl Ar–CH3 2.5 – 2.7 Amine –NH2 1 – 5, variable

Alkyne C H 2.5 – 2.7 Alcohol –OH 1 – 5, variable

Alkyl halide (X = Cl, Br, I) C X

H

2.5 – 4.5 Carboxylic acid –COOH 11.0 – 12.0

Nominal Atomic Masses of Elements Commonly Found in Organic Compounds

H 1 O 16 F 19 I 127 C 12 P 31 Cl 35.5 Li 7 N 14 S 32 Br 80 Mg 24

chem 203 final exam december 11, 2008

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