Q4-35E - Organic Chemistry (Mcmurry)

Question

A 1, 2-cis disubstituted cyclohexane, such as cis-1, 2-dichlorocyclohexane, must have one group axial and one group equatorial. Explain.

Step-by-Step Solution

Answer

For cis relationships either both the groups in an upward or downward direction.

Cis-trans isomerism in cyclohexane

There are four conformations possible for cyclohexane such as a chair, twist boat, boat, half chair. Among all the four conformations chair form of cyclohexane is considered a very stable one. Chair conformation of cyclohexane is as follows;

We simply can say if the relation is up-up then cis, if down–down relationship then trans.

If up-down or down-up relation between the bond then trans.

cis-1, 2-dichlorocyclohexane

The structure of cis-1, 2-dichlorocyclohexane is as follows;

If we observe the structure then it is seen that both the $\text{ - Cl}$groups are in an upward direction hence they show a cis relationship. That is one $\text{ - Cl}$group is in the axial position while the other $\text{ - Cl}$group is in the equatorial position.