Select all correct answers about 1,2-dimethylcyclohexane

a.) The cis-isomer upon ring flip gives another conformation which is equal in energy to itself.

b.) The cis isomer is higher in energy that the e,e conformer

c.) The a,a-conformation of the trans isomer of 1,2-dimethylcyclohexane is equal in energy as the cis isomer.

d.) trans - isomer can be readily converted into the cis-isomer via a ring flip

e.) trans and cis -isomers of 1,2-dimethylcyclohexane are example of constitutional isomers.