Chapter 10.SE, Problem 16VC

Interpretation Introduction

Interpretation:

The alkyl beromide shown is prepared by treating (S)-2-pentanol with PBr₃. The name of the alkyl bromide and its stereochemistry whether R or S are to be stated. Further whether there is any change in stereochemistry during the course of the reaction is also to be stated.

Concept introduction:

The alkyl halides are named using the following guidelines. The longest continuous carbon chain in the molecule is chosen. The chain is numbered from the end which gives lowest number to the substituent either halo or alkyl group present.

For assigning the configuration as R or S, the four groups attached to the chiral carbon are arranged in the order of preference based on the sequence rules. The molecule is viewed by orienting the molecule in such a way that the group of lowest ranking points away from the observer. If the arrangement of the groups of first, second and third ranking (1->2->3-) is clockwise R configuration is assigned. If their arrangement is anti-clockwise then S configuration is assigned.

If both the reactants and products of a reaction have same configuration the reaction is said to occur with retention in stereochemistry. If they have different configurations the reaction is said to occur with inversion in stereochemistry.