Sciencemadness Discussion Board

C-H bond enthalpy in Benzene

Wrecking Bereserker - 23-6-2019 at 11:51

How does the C-H bond dissociation enthalphy in benzene compares to regular sp2 C-H bond(ie:-Alkenes)?

And why are phenyl and vinyl carbo cations less stable?is it because of resonance?

Ubya - 24-6-2019 at 06:22

110 kcal/mol for phenyl C-H and 112kcal/mol for vinyl C-H, pretty much the same.
Phenyl carbocations are less stable because they are not aromatic anymore, they don't have those 35kcal/mol of stabilization. Another reason is the fact that a carbocation of an sp2 carbon wants to be sp (linear) but a 6 membered ring would be strained too much, so this makes it even less stable.
The vinyl carbocation is free to be linear but with the positive charge directly on the "sp2" carbon is not resonance stabilized, only the presence of electron releasing groups can stabilize it