Advices For Studying Organic Chemistry

hydrogen atoms on the same side of the molecule (attached to C3 and C5 atoms)

that the van der Waals forces between them are repulsive.

i) The strain caused by a 1,3-diaxial interaction in methylcyclohexane is the

same as the gauche interaction.

H

H

H H

H

H

H

H

1

3 2

5

6

4

HH

HH C H

H

H HH C H

H

H

H

H

H

1

3 2

5

6

4

H

HHH

H

H C

H

H

H
gauche-Butane Axial methylchclohexane Equatorial methylchclohexane
(3.8 kJ mol–1 steric strain) (two gauche interactions
= 7.6 kJ mol–1 steric strain)

ii) The axial methyl group in methylcyclohexane has two gauche interaction,

and therefore it has of 7.6 kJ mol–1 steric strain.

iii) The equatorial methyl group in methylcyclohexane does not have a gauche

interaction because it is anti to C3 and C5.

4. The conformation of tert-butylcyclohexane with tert-butyl group equatorial is
   more than 21 kJ mol–1 more stable than the axial form.

1. At room temperature, 99.99% of the molecules of tert-butylcyclohexane have
   the tert-butyl group in the equatorial position due to the large energy difference
   between the two conformations.


2. The molecule is not conformationally “locked”. It still flips from one chair
   conformation to the other.