Can you explain to me:

  • What are Cis-Trans, E-Z and Syn-Anti Isomerization?
  • What is the difference between them?
  • How many functional groups is cis-trans isomerism applicable to?

I know mostly about cis trans and E-Z but have no idea about syn- anti isomers. Correct me if needed: I think cis and trans isomers respectively occur when identical atoms or groups are on the same or opposite side of the double bond respectively. E and Z isomers are for trans and cis in complex cases where more functional groups are involved.

Also, I couldn't follow the Wikipedia Link.

  • $\begingroup$ Syn and anti are used more commonly in case of addition to an unsaturated compounds not to denote the actual compounds. $\endgroup$ Mar 27, 2015 at 13:30
  • 3
    $\begingroup$ see this earlier answer $\endgroup$
    – ron
    Mar 27, 2015 at 14:35

1 Answer 1


cis and trans are older notations that express roughly same concept of E and Z.

Explicitly, E and Z have absolute meaning and are assigned based on precedent, where the Z is assigned to the case where the highest priority substituents are on the same side of the alkene/double bond and E being opposite. These notations explicitly refer to a pair wise relationship. It is not normally said '... the group E to the ...'

cis and trans refer to substituents of context, with cis being substituents on the same side of the alkene/double bond, and trans being opposite. Frequently these refer to the most important nomenclaturally, but not always. Additionally cis and trans are used in discussions such as '...the group trans to the ...' describing a relation of one object relative to the other. cis and trans are no longer considered IUPAC-correct nomenclature, but still have some usage for descriptive discussion.

  • $\begingroup$ what is syn anti that is my main question $\endgroup$
    – geek101
    Mar 27, 2015 at 16:40
  • $\begingroup$ Perhaps then, those terms should be first in your list of 'difference between' items. Ron's comment contains a post to an answer which covers syn and anti. $\endgroup$
    – Lighthart
    Mar 27, 2015 at 20:33

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