Why does brom o- 1 butene and bromo 2 butene undergo resonance?
1 Answer
Jun 11, 2018
Well, it's not that THEY do...
I assume you mean these:
But let's consider what this was originally...
-
The proton adds on (as strong acids do to
#pi# bonds!) to the end carbon, so that a#2^@# carbocation forms, instead of a#1^@# one. This merely follows Markovnikov addition. -
The
#"Br"^(-)# could have taken option#(1)# (dashed arrow) and attacked at the cationic carbon... but internal resonance, option#(2)# (solid arrow), is faster than external nucleophilic attack.
Furthermore, since the resonance generates a
#1^@# carbocation (which is known to be among the least stable of the substituted carbocations), the two arrows in option#(2)# are simultaneous, and NOT stepwise---no second intermediate forms.
