The all-trans-1,2,3,4,5,6-hexaethylcyclohexane (1) prefers

Chapter 4, Problem 4.76

(choose chapter or problem)

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, 893894): Et Et Et Et Et Et i-Pr i-Pr i-Pr i-Pr i-Pr i-Pr 1 2 (a) By examining a molecular model of cyclohexane with several alltrans-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. (b) The all-axial conformation of 2 possesses a fairly stable conformation where the steric repulsion among the axial isopropyl groups can be minimized. Again, use models to examine this chair conformation and draw it. Also, draw a Newman projection looking down one of the C!C bonds connecting the cyclohexyl ring to an axial isopropyl group and illustrate why this conformation is lower than the all-equatorial chair conformation in steric destabilization.