Organic Chemistry

PROBLEM 11

Propose a mechanism for each of the following reactions:

a.

b.

c.

PROBLEM 12

Give the major product formed when each of the following alcohols is heated in the

presence of

a. d.

b. e.

c. f.

12.6 Substitution Reactions of Ethers

The group of an etherand the group of an alcohol have nearly the same

basicity, since their conjugate acids have similar values. (The of is

15.5 and the of is 15.7.) Both groups are strong bases, so both are very poor

leaving groups. Consequently, alcohols and ethers are equally unreactive toward

nucleophilic substitution.

Many of the reagents that are used to activate alcohols toward nucleophilic substitution

(e.g., cannot be used to activate ethers. When an alcohol reacts with an

activating agent such as a sulfonyl chloride, a proton dissociates from the intermediate in

the second step of the reaction and a stable sulfonate ester results.

SOCl 2 , PCl 3 )

an alcohol

ROH

an ether

ROR

pKa H 2 O

pKa pKa CH 3 OH

¬OR ¬OH

CH 3 CH 2 CH 2 CH 2 CH 2 OH

OH

CH 3 CH 2 CH CCH 3

CH 3

OH CH 3

CHCH 2 CH 3

OH

CH 2 OH

CH 3 CH 2 C CHCH 3

CH 3

OH CH 3

H 2 SO 4 :

OH

+ HBr

Br

CH 3

CH 3

CH 3

CH 3

H 2 SO 4

O CH^2 OH ∆ O CH^3

∆

H 2 SO 4

CH 3

CH 3

OH

CH 3

CH 3

Section 12.6 Substitution Reactions of Ethers 451

BRUI12-437_480r3 27-03-2003 11:51 AM Page 451