[calverts]

Exam Question:

'Reaction of 1,4-dibromobutane with HSbF6 in methylene chloride under very dry conditions gave a crystalline salt C4H8BrSbF6. This salt is quite stable compared to standard alkyl fluorantimonates, RSbF6. Explain'

I think that the superacid forms a carbocation which is then stabilised by the presence of the bromine via anchimeric assistance and hyperconjugation. But I'm not really sure...

[clarkstill]

I guess it forms something equivalent to a bromonium ion, which I think is what you're getting at. Not sure if hyperconjugation has much to do with it (any more than any other carbocation), but certainly anchimeric stabilization of the carbocation.