Q5-72E - Organic Chemistry (Mcmurry)

Question

Draw both cis- and trans-1,4-dimethylcyclohexane in their more stable chair conformations. 

(a) How many stereoisomers are there of cis-1,4-dimethylcyclohexane, and how many of trans-1,4-dimethylcyclohexane? 

(b) Are any of the structures chiral? 

(c) What are the stereochemical relationships among the various stereoisomers of 1,4-dimethylcyclohexane?

Step-by-Step Solution

Answer

Step 1: Number of stereoisomers

There are one cis isomer and one trans isomer each for 1,4-dimethyl cyclohexane. Cis isomer has two methyl groups on same side and two hydrogen groups on same side. While trans isomer has two methyl groups on different sides. 

Their structures are shown as below:

Step 2: Chirality of stereoisomers

Both cis and trans isomers are chiral because carbon atoms are attached to same groups in both cis and trans isomer.

Step 3: Relationship between the stereoisomers

Both cis and trans compounds are non-superimposable non-mirror images, i.e. diastereoisomers.