# confusion about exocyclic double bond [duplicate]

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

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