Chapter 5.7, Problem 5.26TIY

Interpretation Introduction

Interpretation: The structures of the products of monobromination of $\left(S\right)\text{-2-bromopentane}$ at each carbon atom should be written as well as name of the products, the optically active forms along with their chiral or achiral nature and whether formation will occur in equal or unequal amounts should be identified.

Concept introduction: In order to assign absolute configuration of R and S Cahn − Ingold − Prelog rules are used and the first step is to assign the priority order on the basis of atomic number. The one with highest atomic number gest highest priority and is designated as a and so on.

The Fischer projection is written along with the priorities assigned and groups are interchanged between adjacent places so as to obtain lowest priority group at the bottom or lowest priority.

If the groups now are arranged are read from highest towards least in clockwise fashion the R is assigned to the stereocenter, if the rotation is anticlockwise the S is assigned at the configuration.

Four kinds of symmetry elements that may be present are tabulated as follows:

  $\begin{array}{ccc}\text{S}\text{.No}& \text{Symmetry element}& \text{Notatio}n\\ 1.& \text{Axis of symmetry}& C_n\\ 2.& \text{Plane of symmetry}& \sigma \\ 3.& \begin{array}{l}\text{Alternating axis of }\\ \text{symmetry}\end{array}& S_n\\ 4.& \text{Center of symmetry}& i\end{array}$

The enantiomers are identical chemical compounds that have a mirror-image relationship to each other while diastereomers do not hold mirror image relationships. The former are chiral and optically active while the latter can be chiral or achiral.

Any organic compound must have no plane of symmetry in order to be optically active. The compounds with any plane of symmetry are achiral and optically inactive.