My book (see bottom) implies that hydrohalogenation of 4-methyl-cyclohexene follows this mechanism:
Why not undergo consecutive hydride shifts to furnish a tertiary carbocation?
I would guess that the second step, nucleophilic attack by bromine, is much faster and prevents this from happening. But when I try to confirm this by looking up some examples I see this one at masterorganicchemistry.com:
This implies the following very similar mechanism:
The carbocation in the example is a smaller ring, meaning it should be less stable and even more reactive (less able to perform hydride shifting.) But then again the charge is closer to the tertiary carbon and easier accessible.
Could someone explain what is happening?
Vollhardt, P.; Schore, N. Molecules: Structure and Function, 6th edition; W. H. Freeman: New York, 2014, p491 exercise 12-6:
Predict the outcome of the addition of HBr to (a) 1-hexene; (b) trans-2-pentene; (c) 2-methyl-2-butene; (d) 4-methylcyclohexene. How many isomers can be formed in each case?