Portland State University - - Professor Carl C. Wamser

Chemistry 331 - Fall 1997

Exam 3 Answers

1. (15 points) Write a complete IUPAC name for each of the following compounds, including designation of stereochemistry if it is specifically shown:

a)

5-bromo-2-methylbenzoic acid

b)

1-phenyl-1,1-butanediol (or 1-phenylbutane-1,1-diol)

c)

(1S,3R)-3-methoxy-1-methylcyclopentanethiol

2. (10 points) Arrange the four isomeric butyl bromides (C4H9Br) in order of their expected reactivity in an SN2 reaction.

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. Indicate stereochemistry if it is specific.

a)

b)

c)

d)

e)

4. (15 points) Arrange the following in order with respect to the property indicated. Write "MOST" under the most reactive or highest value and "LEAST" under the least reactive or lowest value.

a) reactivity towards HNO3 / H2SO4

MIDDLE / LEAST / MOST

b) water solubility

MOST / MIDDLE / LEAST

c) nucleophilicity

MIDDLE / MOST / LEAST

d) acidity

MIDDLE / MOST / LEAST

e) cation stability

MIDDLE / LEAST / MOST

5. (15 points) Write a complete mechanism for the acid-catalyzed dehydration of 1-methylcyclohexanol. Show all steps.

What would be the name for the mechanism of this reaction?

E1

Identify which step would be the rate-determining step.

Step 2 - formation of the carbocation is the slowest step

There are two possible products formed (show both). Identify the major product. In which step is the product determined?

Step 3 - loss of H+ determines the position of the double bond

6. (15 points) Write a complete synthetic sequence to illustrate how you could prepare either one of the compounds below starting with benzene.

In your synthesis, show each reaction step with the necessary reagents and conditions, but it is not necessary to show reaction mechanisms.

CHOOSE JUST ONE

7. (15 points) Although a nitro group makes an aromatic ring much less reactive towards electrophilic substitution, a nitro group makes phenol a much stronger acid. Explain why these effects are opposite, specifically including resonance forms for the conjugate base of phenol.

Since nitro is strongly electron-withdrawing, it will deactivate reactivity towards electrophiles, which have a cation intermediate. However, electron withdrawal is favorable for acidity because the reaction generates an anion intermediate (the conjugate base). The effects are opposite because the reactions involve intermediates of opposite charge.

Predict whether m-nitrophenol or p-nitrophenol would be the stronger acid.

p-Nitrophenol is the stronger acid, because the favorable influence of the nitro group will be felt more strongly there, as shown in the resonance forms.