The enantiomers **1a** and **1b** can have their double bonds defined by [CIP rules][1] 1a and 5. Rule 1a dictates that CH<sub>3</sub>>H while Rule 5 has R>S. Thus, **1a** has an *E*-double bond  and **1b** is of the *Z*-configuration as exemplified by the red bonds. [This issue has been addressed previously on this site][2].<br><br>


<img src="https://i.sstatic.net/LS5kE.jpg" height="200">


  [1]: http://ursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/isomers/CIP%20rules%20NEW.html
  [2]: https://chemistry.stackexchange.com/questions/58630/why-is-1-ethylidene-4-methylcyclohexane-chiral/96265#96265