Advices For Studying Organic Chemistry

i) The cylohexane ring rapidly flips back and forth between two equivalent chair

conformation via partial rotations of C—C bonds.

ii) When the ring flips, all of the bonds that were axial become equatorial and

vice versa.

Axial

ring

flip

Axial

1

(^432)
(^56) Equatorial
Equatorial
3 2 1
4 5 6

3. The most stable conformation of substituted chclohexanes:
   
   
   1. There are two possible chair conformations of methylcyclohexane.
   
   
   
   

(1)

(axial)

H

H

H

CH 3

H

H

H

H

H

H

HCH 3

H

H

H

CH 3

H

H

H

H

H

H

HCH 3

(equitorial)

(less stable)

(2)

(more stable by 7.5 kJ mol−1)

H

H

H

H

HH

H

H

H

H

H

H

(a)

H

H

H

H

HH

H

H

H

H

H

H

1

3

5

(b)

Figure 4.20 (a) The conformations of methylcyclohexane with the methyl group
axial (1) and and equatorial (2). (b) 1,3-Diaxial interactions between
the two axial hydrogen atoms and the axial methyl group in the axial
conformation of methylcylohexane are shown with dashed arrows.
Less crowding occurs in the equatorial conformation.

2) The conformation of methylcyclohexane with an equatorial methyl group is

more stable than the conformation with an axial methyl group by 7.6 kJ mol–1.