Advices For Studying Organic Chemistry

ii) The base can attack either of these hydrogen atoms and achieve an anti

periplannar transition state for an E2 reaction.

ii) Products corresponding to each of these transition states (2-menthene and

1-menthene) are formed rapidly.

v) 1-Menthene (with the more highly substituted double bond) is the major

product (Zaitsev’s rule).

A Mechanism for the Elimination Reaction of Neomenthyl Chloride

E2 Elimination Where There Are Two Axial Cyclohexane β-Hydrogens

1

4 3 2

Et−O −

Et−O −

(a)

(a)

(b)

(b)

H 3 CC 1 H(CH 3 ) 2

3 2

4

H 3 C 1 CH(CH 3 ) 2

3 2

4

1-Menthene (78%)

(more stable alkene)

2-Menthene (22%)

(less stable alkene)

Neomenthyl chloride

H

Cl

H

H

Both green hydrogens are anti to the

chlorine in this the more stable

conformatio. Elimination by path (a) leads

to 1-menthene; by path (b) to 2-menthene.

H

H 3 C CH(CH 3 ) 2

(^)