Question 26.5: Predicting Which Conformer of a Disubstituted Cycloalkane Is...
Predicting Which Conformer of a Disubstituted Cycloalkane Is Lowest in Energy
Draw the lowest energy conformation of cis-1,3-dimethylcyclohexane.
Analyze
First, we draw a cyclohexane ring showing both the axial and the equatorial bonds but without the substituents added to the ring. Then, we consider the placement of the substituents. A useful tip is to realize that when the carbon atoms in a cyclohexane ring are numbered, there is a relationship between the bonds on the odd- and even-numbered carbon atoms. When the odd-numbered carbons have their up bonds axial, the even-numbered carbon atoms have their down bonds axial. When the odd-numbered carbons have their up bonds equatorial, the even-numbered carbons have their down bonds equatorial. The relationship is illustrated in the diagram below:
