Advices For Studying Organic Chemistry

1. The highly strained three-membered ring of epoxides makes them much more
   reactive toward nucleophilic substitution than other ethers.

1. Acid catalysis assists epoxide ring opening by providing a better leaving group
   (an alcohol) at the carbon atom undergoing nucleophilic attack.

2. Epoxides Can undergo base-catalyzed ring opening:

A Mechanism for the Reaction

Base-Catalyzed Ring Opening of an Epoxide

CC

O

RO −+ RO O − RO OH

OR

RO −

CC CC

+

H

Strong

nucleophile Epoxide An alkoxide ion

A strong nucleophile such as an alkoxide ion or a hydroxide ion is able to open the

strained epoxide ring in a direct S N2 reaction.

1) If the epoxide is unsymmetrical, the nucleophile attacks primarily at the less

substituted carbon atom in base-catalyzed ring opening.

H 2 CCHCH 3

O

O −

O

H 3 CH 2 CO − H 3 CH 2 CO

H 3 CH 2 CO

+

OCH 2 CH 3

H 3 CH 2 CO −

CH 2 CH

CH 3

CH 2 CH

CH 3

H +

H

Methyloxirane

1-Ethoxy-2-propanol

1 o Carbon atom is less hindered

2) If the epoxide is unsymmetrical, the nucleophile attacks primarily at the more

substituted carbon atom in acid-catalyzed ring opening.