Concepts: in cyclohexane ring itself, there can be two conformers by the ring flipping and Both are equivalent in terms of energy since there are always six hydrogens in axial position and six hydrogens in equatorial position.
However, for substituted cyclohexane the two chair conformations are not equivalent any more. As given above in structure I the R group is at axial position and in Structure II the R group is at equatorial position. Studies show that the conformer II with the equatorial R group is more stable.
This difference in stability is due to the “1,3-diaxal interaction”. In axial R group conformation, the R group is very close to the axial hydrogens that is one carbon away and it causes the repulsion between each other that is called the 1,3-diaxal interaction.
This type of repulsion is the same as the gauche steric strain because the R group and the CH are in gauche position. While for equatorial- R group conformer, no such strains applied because the R group and the CH are in anti-position.
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