Organic Chemistry

acid immediately donates a proton to the amine when the two compounds are mixed.
The ammonium carboxylate salt is the final product of the reaction; the carboxylate ion
is unreactive and the protonated amine is not a nucleophile.

PROBLEM 27

Using an alcohol for one method and an alkyl halide for the other, show two ways to make

each of the following esters:

a. methyl butyrate (odor of apples) d. octyl acetate (odor of oranges)

b. propyl acetate (odor of pears) e. isopentyl acetate (odor of bananas)

c. ethyl butyrate (odor of pineapple) f. methyl phenylethanoate (odor of honey)

PROBLEM-SOLVING STRATEGY

Propose a mechanism for the following reaction:

When you are asked to propose a mechanism, look carefully at the reagents to determine the

first step of the mechanism. One of the reagents has two functional groups: a carboxyl group

and a carbon–carbon double bond. The other reagent, does not react with carboxylic

acids, but does react with alkenes (Section 4.7). One side of the alkene is sterically hindered

by the carboxyl group. Therefore, will add to the other side of the double bond, forming

a bromonium ion. We know that in the second step of the addition reaction, a nucleophile will

attack the bromonium ion. Of the two nucleophiles present, the carbonyl oxygen is posi-

tioned to attack the back side of the bromonium ion, resulting in a compound with the

observed configuration. Loss of a proton gives the final product of the reaction.

Now continue on to Problem 28.

PROBLEM 28

Propose a mechanism for the following reaction. (Hint:Number the carbons to help you

see where they end up in the product.)

C

O

CH 3 O

CH 2 CHCH 2 CH 2 CH CCH 3 CH 3 COH H^2 SO^4

H 3 C

CH 3

+ OCH 3

Br 2

Br 2 ,

Br 2

O CH^2 Cl^2 O + HBr

O

Br

OH

an ammonium

carboxylate salt

CH 3

+

CH 3

CH 3 CH 2 NH 2

CH 3 CH 2

+

CH 3 CH 2

NH 3

O−

O−

+

+

OH H 3 NCH 2 CH 3

OH NH 4

C

O

C

O

C

O

C

O

HBr

Br

O

Br + Br−

OH

OO

Br Br

OH

O

OH

O

Br

+

+

+

Section 17.14 Reactions of Carboxylic Acids 703