Chapter 10, Problem 22P

Interpretation Introduction

Interpretation:

The compounds that are likely to be formed on free-radical addition of $\text{HBr}$ to $\text{cis-2-pentene}$ are to be determined and the stereochemically accurate formula for each of them is to be written, and the configuration at each chirality center is to be specified.

Concept introduction:

The number of stereoisomers formed can be calculated using the formula $2^n$, where $n$ is the number of chiral centers present in the molecule.

The absolute configuration of the chiral center is determined on the basis of the following rules:

First priority of the four groups present on the carbon atoms is decided. Higher is the atomic number of the group, higher is its priority.

The compound undergoes rotation in order to get the least priority group above or below the plane.

If the least priority group is present below the plane, then clockwise arrangement of first three priority groups gives R configuration and anticlockwise gives S. Reverse is true if the least priority group is present above the plane.