How would you call a pair of isomers on the picture below? enter image description here

They look a lot like regular cis/trans isomers, except all four groups are different. I can tell they are spacial isomers (stereoisomers) but is there a more specific name for this kind of isomerism?

  • 3
    $\begingroup$ Check : Cahn-Ingold-Prelog priority rules $\endgroup$
    – TheLearner
    Apr 6, 2019 at 0:01
  • 8
    $\begingroup$ Cis-trans is generalised as E/Z. $\endgroup$
    – Mithoron
    Apr 6, 2019 at 0:17

1 Answer 1


When all four substituents are different cis-trans type of isomerism cannot be applied. Moreover the Cis trans system is often ambiguous because configurational descriptions have not been defined according to any general and clear set of rules. For these types, there is system called E-Z system of nomenclature and is based on the sequence rules of Cahn, Ingold and Prelog (CIP) rule, originally developed for naming optical isomers on R-S system


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