The all-trans-1,2,3,4,5,6-hexaethylcyclohexane ( 1) prefers the all-equatorial conformation while the all-trans-1,2,3,4,5,6-hexaisopropylcyclohexane (2) possesses a severely destabilized all-equatorial conformation (J. Am. Chem. Soc. 1990, 112, 893–894):
(a) By examining a molecular model of cyclohexane with several all trans-equatorial isopropyl groups and another model with several all-trans-equatorial ethyl groups, determine why adjacent equatorially oriented isopropyl groups experience severe steric interactions which are lacking in the ethyl case. Draw a chair conformation of the former case which illustrates these severe steric interactions. Also draw a Newman projection looking down one of the C—C bonds connecting the cyclohexyl ring to an equatorial isopropyl group and illustrate a conformation with severe steric strain.