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Substituted Cyclohexanes
Substituents on cyclohexane can, in principle, occupy either axial or equatorial positions. However, in general, equatorial substituents are more preferred since they are more stable because of reduced steric interactions.
This is shown in the following example for methycyclohexane.
In the equatorial system, the methyl group is anti to the C-C
bonds in the rest of the ring system. However, in the axial conformation,
a steric interaction of the methyl group with the two axial hydrogen atoms
on the same face of the ring destabilizes the axial conformation. In the
images below, this 1,3-diaxial interaction can be highlighted
and contrasted with the equatorial conformer. The effect is most obvious
when viewed in the space filling model.
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The larger the alkyl substituent is, the greater the preference for the equatorial position since the larger the group the greater the steric interaction with the axial hydrogens.
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