Chapter 11, Problem 11.9P

Interpretation Introduction

Interpretation:

The complete mechanism for the formation of all products with stereochemistry in the given reaction is to be drawn.

Concept introduction:

The electrophilic addition of a Bronsted acid to the carbon-carbon double bond in alkenes is susceptible to carbocation rearrangements due to the stability of the carbocation. The carbocation rearrangement occurs via either 1, 2 hydride shift or 1, 2 methyl shift depending on the stability of the carbocation formed. The stability order for carbocation is benzylic > tertiary > secondary > primary > methyl etc. The normal electrophilic addition gives 1, 2-addition product, but due to rearrangement reaction, the rearranged product may be formed instead of the 1, 2-addition product. In the reaction of an alkene and hydrogen halide or deuterium halide, the carbon to which the deuterium is attached is the carbon bearing the positive charge, and the carbon atom to which the halide atom is attached must be the carbon bearing the positive charge, that is, carbocation intermediate. Rearrangements of the carbocation intermediate may be observed if a more stable carbocation is possible. When a proton adds to the carbon-carbon double bond of an asymmetric alkene, two carbocation intermediates may be formed. One of them will be more stable, leading to give the major addition product. According to the Markovnikov rule, the proton adds to the alkene carbon that is initially bonded to the greater number of hydrogen atoms because it leads to form a more stable carbocation as intermediate.

Due to the formation of the planar carbocation intermediate, the attack of the nucleophile takes place either from the top or from the bottom of the plane, giving a mixture of isomers, if the reaction takes place on the chiral center.