This question already has an answer here:

enter image description here

I believe that there are only two exocyclic bonds in this structure. But in some text its mentioned as three. can someone clarify.


marked as duplicate by Mithoron, Todd Minehardt, Jon Custer, Tyberius, A.K. Dec 6 '18 at 19:03

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ IMHO there are total zero exocyclic bonds. $\endgroup$ – mykhal Dec 5 '18 at 10:28
  • $\begingroup$ I agree. Exocyclic means outside the ring structure; the double bonds are all within the ring structure $\endgroup$ – Waylander Dec 5 '18 at 10:39
  • $\begingroup$ but, ring B has two exocyclic bonds $\endgroup$ – RZZ Dec 5 '18 at 10:58
  • $\begingroup$ @RZZ …relative to that ring. yes, but they are still in another ring. It depends on the term exocyclic bond purpose and context. $\endgroup$ – mykhal Dec 5 '18 at 11:06
  • $\begingroup$ ok. so for the purpose of calculating the Lambda max using woodward fieser rule. how many do you think are there? $\endgroup$ – RZZ Dec 5 '18 at 11:15

By definition (in Woodward-Fieser rule), an exocyclic double bond is a double bond where one of the $sp^2$ carbon atoms of the bond is a part of a ring, while the other $sp^2$ carbon of the bond is not a part of same ring (it could be a part of another ring).

If both the $sp^2$ carbon atoms of the double bond is part of the same ring, then it is called endocyclic double bond. From these definitions, you can understand that exocyclic would stand for a double bond outside the ring and endocyclic would stand for a double bond within the ring. Following examples would illustrate the definition:

enter image description here

  • $\begingroup$ yup!! agreed. so now according to this definition how many exocyclic double bonds are there in the structure i posted? $\endgroup$ – RZZ Dec 6 '18 at 6:07
  • $\begingroup$ You may count it by yourself. You'd learn by that. $\endgroup$ – Mathew Mahindaratne Dec 6 '18 at 22:28
  • $\begingroup$ Three is the correct answer. One double bond is exocyclic to both cyclopentyl and cyclohexyl rings. $\endgroup$ – Mathew Mahindaratne Dec 6 '18 at 23:08

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