Chapter 4, Problem 4.29P

Interpretation Introduction

(a)

Interpretation:

The Newman projections of $\text{cis-1, 2-dimethylcyclopropane}$ and $\text{trans-1, 2-dimethylcyclopropane}$ are to be drawn.

Concept introduction:

A Newman projection visualizes the conformation of a molecule about a chemical bond from front to back. The front carbon is represented by a dot and back carbon by a circle. Then remaining atoms would be drawn as they are attached to respective carbon atoms. The bonds to the front carbon converge on the dot while the bonds to the back carbon end at the circle.

Interpretation Introduction

(b)

Interpretation:

The more stable configuration out of the two shown is to be identified.

Concept introduction:

The stability of cyclic hydrocarbons depends on two factors – ring strain and torsional strain. With only three ring carbons, the ring is an equilateral triangle, with ${60}^{\text{o}}$ bond angles. The bonds to all the atoms/groups attached to the ring are eclipsed bonds, which also introduce considerable torsional strain.