I am currently learning about Alkenes. It is given that cis/trans isomerism is either ambiguous or doesn't even apply in cases where the alkene is trisubstituted or tetrasubstituted. To solve this problem, we make use of the E/Z system of classifying the diastereomers of alkenes. In some cases both the methods of classifying diastereomers works.

My doubt is, why are we still using cis/trans system while the E/Z system is better than it? Is the cis/trans system better than E/Z system in some way?

  • $\begingroup$ Not really. It is just that we got used to it. $\endgroup$ Oct 9, 2019 at 13:24
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    $\begingroup$ cis/trans applies to concepts other than alkenes. Since you're describing similar relationships with cis/trans, the term is still valid with alkenes. $\endgroup$
    – Zhe
    Oct 9, 2019 at 14:11

2 Answers 2


That is because the E/Z-system is an extension of the cis/trans-system. So both systems can be applied to a certain amount of structures and the E/Z-system is then able to treat more advanced systems.

From my perception, it seems that Chemistry is a very stubborn … or maybe just very conservative … field where especially new naming conventions get hardly accepted. At least not very fast. So we are still using Angstrom instead of nanometer or picometer and so on. This also means that we stick with the cis/trans-system as long as it fits and we only change in case we can’t apply it.

  • $\begingroup$ Ångstrom is 1e-10 so maybe you will get extra zeroes or have to prepend decimal places in certain disciplines $\endgroup$
    – Mark C
    Jun 12 at 3:15

cis and trans are perfectly valid descriptors for linear disubstituted alkenes. The (E) and (Z) system is more comprehensive for alkenes, as it also covers trisubstituted and tetrasubstituted alkenes which cis/trans by definition cannot (although some might extend it anyway).

In most cases, it would be perfectly reasonable and possible to replace every alkenic cis/trans with a corresponding (E)/(Z). However, in practice cis and trans prevail for no other reason that ‘we did it before’ in a lot of contexts and systems. For example, Aldrich sells trans-cinnamic acid.

When you are not dealing with alkenes, but with coordination compounds, cis/trans cannot be replaced by (E)/(Z) as far as I am aware. Since it remains in use there, there is no harm in teaching it in other places, too.


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