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Carbo-cations may be stabilized by:
(a) π-bonds only at allylic position
(b) π-bonds only at vinylic position
(c) π-bonds at allylic and benzylic position also (d) -I effect

While the answer is obviously not (d), I am really confused about what 'allylic', 'vinylic' and 'benzylic' positions actually mean. I have heard about allylic/vinylic/benzylic carbons, but positions..?

Please, help.
Thank-you.




The question has been taken from ADVANCED PROBLEMS IN ORGANIC CHEMISTRY by HIMANSHU PANDEY

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For carbocation stability, think about which case has opportunity for electron resonance, i.e., which case(s) allows the positive charge to be delocalized to adjacent pi bonds. This resource might help.

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Allylic position is the same as allylic carbon....similarly for vinylic and benzylic...so the stability of carbocations goes as

benzylic > allylic > vinylic vinyl carbocations moreover are highly unstable...whereas the other two are rather stable ones...and the answer is (C) enter image description here enter image description here

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