Advices For Studying Organic Chemistry

H CH 3

H CH 3

H H

CH 3 CH (^3)
cis-1,2-Dimethylcyclopentane trans-1,2-Dimethylcyclopentane
bp 99.5 °C bp 91.9 °C
Figure 4.22 cis- and trans-1,2-Dimethylcyclopentanes.
H H
CH 3
CH 3 H
H
CH 3 CH (^3)
cis-1,3-Dimethylcyclopentane trans-1,3-Dimethylcyclopentane

1. The cis- and trans-1,2-dimethylcyclopentanes are stereoisomers; the cis- and
   trans-1,3-dimethylcyclopentanes are stereoisomers.

1. The physical properties of cis-trans isomers are different: they have different
   melting points, boiling points, and so on.

Table 4.8 The Physical Constants of Cis- and Taans-Disubstituted

Cyclohexane Derivatives

Substituents Isomer mp (°C) bp (°C)a

1,2-Dimethyl- cis –50.1 130.04^760

1,2-Dimethyl- trans –89.4 123.7^760

1,3-Dimethyl- cis –75.6 120.1^760

1,3-Dimethyl- trans –90.1 123.5^760

1,2-Dichloro- cis –6 93.5^22

1,2-Dichloro- trans –7 74.7^16

aThe pressures (in units of torr) at which the boiling points were measured

are given as superscripts.