I am new to organic chemistry and am confused regarding the following question:

Does the geometrical isomerism of 3-methyl-2-heptene fall into the category of trans vs. cis, or the category of Z vs. E? And what is the rule that determines whether it falls into the first or the second category?

My textbook is not clear on this.

Many thanks!

  • $\begingroup$ Thank you! The thing is that it says somewhere in my notes that cis vs. trans requires there to be two H atoms, obviously on opposite sides of the double bond. This is of course not the case here. Yet I cannot find any external support for this "rule" that miraculously made it into my notes… $\endgroup$
    – dalta
    Jul 16, 2019 at 12:38
  • $\begingroup$ That rule in this context is correct. The corresponding wording in the current IUPAC recommendations is: "… 'cis' and 'trans' are used … only to describe double bonds having to hydrogen atoms, one on each carbon atom. …" $\endgroup$
    – user7951
    Jul 16, 2019 at 18:39

1 Answer 1


(Z) is the same like cis

(E) is the same like trans

BUT cis and trans is usually only for double bonds with 2 different substituents. Confusion can arise when, for instance, you have 2-halobut-2-enes, because some take the highest priority when determining if this is cis or trans whereas others may take the identical groups.

You can use (Z) and (E) for more than 2 substituents, for those with higher priority. Like in your example.

In general it is better to use (Z) and (E) nomenclature to avoid these ambiguities.


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