Conformational Analysis of Monosubstituted Cyclohexanes

Ring inversion in methylcyclohexane differs from that of cyclohexane in that the two chair conformations are not equivalent, hi one chair the methyl group is axial in the other it is equatorial. At room temperature approximately 95% of the molecules of methylcyclohexane are in the chair conformation that has an equatorial methyl group whereas only 5% of the molecules have an axial methyl group. 

See the box entitled Enthalpy, Free Energy, and Equilibrium Constant accompanying this section for a discussion of these relationships. 

Make a molecular model of each chair conformation of methylcyclohexane, and compare their energies. 

When two conformations of a molecule are in equilibrium with each other, the one with the lower free energy predominates. Why is equatorial methylcyclohexane more stable than axial methylcyclohexane  

Van der Waals strain between hydrogen of axial CH3 and axial hydrogens at C-3 and C-5 

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Conformations of Cyclobutane and Cyclopentane Conformations of Cyclohexane 127 Axial and Equatorial Bonds in Cyclohexane 129 Conformational Mobility of Cyclohexane 131 Conformations of Monosubstituted Cyclohexanes Conformational Analysis of Disubstituted Cyclohexanes Boat Cyclohexane 140 Conformations of Polycyclic Molecules 141... 

In opposition to a central principle of alicyclic conformational analysis, Kang and Yin reported that a complex O-cyclohexyl nitronate and the corresponding O-cyclohexyloxime constitute the first stable axial conformer of monosubstituted cyclohexanes at ambient temperature (97JA8562). Snyder and co-workers (99JA11864) reevaluated the corresponding... 

Although analysis of the consequences of ring flip in a monosubstituted cyclohexane is pretty straightforward, the presence of two or more substituents requires careful consideration to decide which conformer, if any, is the more favoured. Let us illustrate the approach using 1,4-dimethylcyclohexane. Now, two configurational isomers of this structure can exist, namely trans and... 

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