text: Entropy also plays a role in a substituent's preference for the equatorial position.  The entropic component is determined by the following formula:
  Where σ is equal to the number of microstates available for each conformation.
  Due to the larger number of possible conformations of ethyl cyclohexane, the A value is reduced from what would be predicted based purely on enthalpic terms.  Due to these favorable entropic conditions, the steric relevance of an ethyl group is similar to that of a methyl substituent.