Chapter 8.3, Problem 6P

Interpretation Introduction

Interpretation:

Given that, when an unsymmetrical alkene such as propene is treated with NBS in aqueous dimethyl sulfoxide, the major product has the bromine atom bonded to the less highly substituted carbon atom. Whether the orientation is Markovnikov or non-Markovnikov is to be explained.

Concept introduction:

NBS can be used as a source of bromine, as it is stable, easily handled compound that slowly decompose in aqueous dimethyl sulfoxide to yield bromine at controlled rate. Bromine from NBS adds on to the double bond to give a cyclic bromonium ion. Water, being a nucleophile, attacks the bromonium ion from the unshielded side to give an intermediate which loses a proton to yield a bromohydrin as the product. The addition occurs with anti stereochemistry.

According to Markovnikov rule, in the addition of HX to unsymmetrical alkenes the H (positive part) attaches itself to the carbon with fewer alkyl substituents and X (negative part) attaches itself to the carbon with more alkyl substituents.

To explain:

Whether the orientation of groups in the addition reaction between propene and NBS in aqueous dimethyl sulfoxide ,where in the major product has the bromine atom bonded to the less highly substituted carbon atom, is Markovnikov or non-Markovnikov.