Organic Chemistry
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Professor Carl C. Wamser

Chem 334 - Fall 2003

EXAM 2 Answers

1. (15 points) Write complete names for each of the following, including stereochemistry if it is specifically shown.

a)

cis-4-methyl-2,5-cycloheptadienol

b)

(Z)-5-bromo-4-(2-cyclobutenyl)-4-penten-1,2-diol

c)

(E)-5-(bromomethyl)-2-cyclohexyl-6-methyl-5-octen-4-ol

2. (15 points) Arrange each of the following in order with respect to the property indicated.
Write “MOST” under the compound with the highest value and “LEAST” under the compound with the lowest value.

a) stability

isobutyl cation < sec-butyl cation < tert-butyl cation

LEAST < MIDDLE < MOST

b) rate of dehydration

isobutyl alcohol < sec-butyl alcohol < tert-butyl alcohol

LEAST < MIDDLE < MOST

c) boiling point

isobutyl alcohol > isobutyl chloride> isobutane

MOST > MIDDLE > LEAST

d) rate of reaction with cyclohexene

F2 > Cl2 > Br2

MOST > MIDDLE > LEAST

e) rate of reaction with cyclohexane

F2 > Cl2 > Br2

MOST > MIDDLE > LEAST

3. (15 points) Complete each of the following reactions by adding the missing part: either the starting compound, the necessary reagents and conditions, or the final major product. Show stereochemistry if it is specific.

a)

b)

c)

d)

e)

4. (10 points) A hypothetical reaction between chlorine and 2,2-dimethylpropane is shown below.
Calculate ΔH for this reaction.

ΔH = 80 + 58 - 79 - 83.5 = - 24.5 kcal/mol
or ΔH = 334 + 242 - 330 - 349 = - 103 kJ/mol

In fact, a different reaction takes place. Write it out as a balanced reaction and calculate ΔH.

ΔH = 98 + 58 - 82 -103 = - 29 kcal/mol
or ΔH = 410 + 242 - 343 - 431 = - 122 kJ/mol

5. (10 points) Strong acid can have the function of isomerizing alkenes, as shown below. Write a mechanism.

Another isomerization catalyzed by strong acid is shown below. Write a mechanism.

6. (15 points) Elimination from 1-iodo-4-methylcyclohexane follows the E2 mechanism when treated with KOH in ethanol. Write the conformation (chair) in which the cis isomer undergoes E2 elimination and illustrate the mechanism using electron-pushing arrows.

Predict whether the trans isomer would undergo E2 elimination faster or slower than the cis isomer. Explain your reasoning.
The trans isomer will react slower. E2 elimination must occur when the iodo group is axial. In the trans isomer, the methyl group will also be axial at the same time, so the reactive conformation will be more unstable than in the cis and will occur less often.

7. (10 points) Write a complete mechanism for the radical chain polymerization of propene.
Start with a general peroxide as initiator ( R-O-O-R ) and show all initiation and at least two propagation steps.

8. (10 points) Photoinduced chlorination of 2,4-dimethylpentane can give three different products having a single chloro substituent.
Write structures for all three and predict the relative amounts of each, using a relative reactivity of 3° > 2° > 1° hydrogens as 5 : 4 : 1 .