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Unformatted text preview: ddition of HX to Alkenes
Mechanism Mechanism of Addition of HX to Alkenes
Step 1. Protonation. This step is slow and rate determining.
Protonation gives the most stable cation. Therefore the
proton adds to the alkene carbon that initially has the
most protons. Mechanism of Addition of HX to Alkenes
Step 2. Combination of the anion and cation. In the rapid second step the bromide attaches to the
carbocation. Potential Energy Graph for Addition of HBr
Carbocation Rearrangements in
Hydrogen Halide Addition to
Alkenes Carbocation Rearrangements
Carbocations rearrange to form more stable cations. The
fact that rearrangements occur on addition of HX to alkenes
provides further support for the reaction mechanism. Carbocation Rearrangements The mechanism must explain the formation of both products.
Here it involves a hydride shift. The final step has chloride attaching to either of the
secondary or tertiary carbocations....
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