Chapter 5.1, Problem 5.5E

(a)

Interpretation Introduction

Interpretation:The structures of two constitutional isomers of bromochloropropane formed upon radical bromination of $\text{2-bromopropane}$ should be written and the chiral and achiral forms should be identified.

Concept introduction: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.

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

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

Presence of any symmetry element makes molecule achiral and optically inactive.

(b)

Interpretation Introduction

Interpretation: The structures of all possible forms of dimethylcyclobutanes should be written, the chiral structures should be specified and mirror planes for achiral ones should be drawn.

Concept introduction: 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 chiral or optically active. The compounds with any plane of symmetry are achiral and optically inactive.

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

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

Presence of any symmetry element makes molecule achiral and optically inactive.