Chapter 4, Problem 4.5P

Interpretation Introduction

Interpretation:

Among $\text{1, 2-dibromoethane}$ and $\text{1, 2-difluoroethane}$, the molecule having larger rotational energy barrier about the C-C bond is to be determined and explained.

Concept introduction:

A rotational energy barrier between two conformations is the difference in energy between the beginning conformation and the highest energy conformation through which the molecule must pass to arrive at the ending conformation. At room temperature, staggered conformations of ethane constantly interconvert through rotation about the C-C single bond.

Electron repulsions between atoms or groups of atoms that are not directly bonded together but occupy the same space results in the increase in energy, which is known as steric strain.