Advices For Studying Organic Chemistry

H

H

H

H

C

H

H

H

H

H

H

HC

CH 3

CH 3

CH 3

H 3 C CH^3 CH 3

H

H

H

HH

H

H

H

H

H

H

Equatorial tert-butylcyclohexane Axial tert-butylcyclohexane

ring flip

Figure 4.21 Diaxial interactions with the large tert-butyl group axial cause the
conformation with the tert-butyl group equatorial to be the
predominant one to the extent of 99.99%.

5. There is generally less repulsive interaction when the groups are equatorial.

Table 4-3 Steric strain due to 1,3-diaxial interactions

Y (Strain of one kcal/mol) (H–Y 1,3-diaxial interaction kJ/mol)

H Y

(^321)
–F 0.12 0.5
–Cl 0.25 1.4
–Br 0.25 1.4
–OH 0.5 2.1
–CH 3 0.9 3.8
–CH 2 CH 3 0.95 4.0
–CH(CH 3 ) 2 1.1 4.6
–C(CH 3 ) 3 2.7 11.3
–C 6 H 5 1.5 6.3
–COOH 0.7 2.9
–CN 0.1 0.4

4.14 DISUBSTITUTED CYCLOHEXANES: CIS-TRANS ISOMERISM

1. Cis-trans isomerism: