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258 CHAPTER 8 
 
8.44. 
(a) Water (H and OH) is added across the alkene in a 
Markovnikov fashion. The mechanism is expected to 
have three steps: 1) proton transfer, 2) nucleophilic 
attack, and 3) proton transfer. In the first step, a proton 
is transferred from H3O+ to the alkene, which requires 
two curved arrows, as shown below. The resulting 
tertiary carbocation is then captured by a water molecule 
in the second step of the mechanism. This step requires 
one curved arrow, going from the nucleophile (water) to 
the electrophile (the carbocation). Then, in the final step 
of the mechanism, a molecule of water functions as a 
base and removes a proton, thereby generating the 
product. This final step is a proton transfer step, and 
therefore requires two curved arrows, as shown: 
 
 
 
 
(b) In the first step of the mechanism, a proton is 
transferred from H3O+ to the alkene, which requires two 
curved arrows, as shown below. The resulting secondary 
carbocation then rearranges via a hydride shift, giving a 
more stable, tertiary carbocation. That step is shown 
with one curved arrow. The tertiary carbocation is then 
captured by a water molecule, which is shown with one 
curved arrow, going from the nucleophile (water) to the 
electrophile (the carbocation). Then, in the final step of 
the mechanism, a molecule of water functions as a base 
and removes a proton, thereby generating the product. 
This final step is a proton transfer step, and therefore 
requires two curved arrows, as shown: 
 
 
 
(c) In this reaction, H and Br are added across the alkene 
in a Markovnikov addition, which indicates an ionic 
process. There are two mechanistic steps in the ionic 
addition of HBr across an alkene: 1) proton transfer, 
followed by 2) nucleophilic attack. In the first step, a 
proton is transferred from HBr to the alkene, which 
requires two curved arrows, as shown below. The 
resulting tertiary carbocation is then captured by a 
bromide ion in the second step of the mechanism. This 
step requires one curved arrow, going from the 
nucleophile to the electrophile, as shown: 
 
 
 
 
(d) Protonation of the alkene requires two curved arrows, 
as shown, and leads to the secondary carbocation (rather 
than a primary carbocation). This secondary carbocation 
then undergoes a methyl shift, shown with one curved 
arrow, generating a more stable, tertiary carbocation. In 
the final step of the mechanism (nucleophilic attack), the 
carbocation is captured by a bromide ion. This step 
requires one curved arrow, going from the nucleophile 
(bromide) to the electrophile (the carbocation), as shown: 
 
 
 
 
8.45. The starting material (1-bromo-1-
methylcyclohexane) is a tertiary alkyl halide, and will 
undergo an E2 reaction when treated with a strong base 
such as methoxide, to give the more substituted alkene 
(compound A). Hydrogenation of compound A gives 
methylcyclohexane: 
 
 
 
 
8.46. 
(a) The desired transformation can be achieved via a 
two-step process (addition, followed by elimination). 
We must be careful to control the regiochemical outcome 
of each step of the process. During the addition reaction, 
we want to install Br at the more-substituted (tertiary) 
position, so we treat the alkene with HBr (without 
peroxides present). Then, the elimination process must 
be performed in a way that gives the more-substituted 
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