Level 1 – Case 11
76
In Summary
As expected, the hydrolysis (solvolysis) of p-substituted styrene oxides follows a
different mechanism in acidic or basic conditions. At low pH values the reaction is
a specific acid-catalyzed process and a carbocation is involved as intermediate.
Under basic conditions, the hydrolysis is nucleophile-catalyzed and the attack of
the nucleophile takes place at both carbons of the oxirane ring. The D-attack
(more hindered position) is preferred when strong p-electron-donating substituents
are placed in the styrene ring. p-Electron-withdrawing substituents favor the Eattack (less-hindered position).
O
Ar
H
OR
O O
Ar
H
RO
-
CH 2 O
Ar
H
OR
ROH
CH 2 OH
Ar
OR
H
-
OR
O O
Ar
H
RO
CH 2 OR
Ar
H
O
CH 2 OR
Ar
H
OH
ROH
D-attack
E-attack
D
E
1
G
-
G
-
G
-
G G
G
-
G
+
R = H, Me
8
9
O
1
Ar = p-MeOC 6 H 4
Ar = p-ClC 6 H 4 , p-NO 2
O O C 6 H 4
Scheme 11.7
Question
Design an experiment to trap the carbocation intermediate. Discuss the structure of
the most appropriate substrate, the type of solvent and propose a suitable trapping
agent.