0
$\begingroup$

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!

$\endgroup$
  • $\begingroup$ 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 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. …" $\endgroup$ – Loong Jul 16 at 18:39
-1
$\begingroup$

(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.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.