Chapter 4, Problem 4.5YT

Interpretation Introduction

Interpretation:

A molecule of ethane (${\text{H}}_{\text{3}}{\text{C-CH}}_{\text{3}}$) using a molecular modeling kit is to be constructed. The $\text{C-C}$ bond is rotated so that the molecule is in an eclipsed conformation. Again the $\text{C-C}$ bond is rotated so that now it is in a staggered conformation. Whether the $\text{C-H}$ bonds are closer in the staggered conformation or in the eclipsed conformation is to be explained.

Concept introduction:

In Eclipsed conformations, the $\text{C-H}$ bonds on the front carbon atom cover or eclipse those on the rear carbon atom in the Newman projections. In staggered conformations, each $\text{C-H}$ bond on the front carbon atom bisects a pair of $\text{C-H}$ bonds on the rear carbon, so the bonds to the front and rear carbon atoms alternate around the circle. In the staggered conformation, repulsion among the electrons in the $\text{C-H}$ bonds is at a minimum, making this the more stable conformation. In the eclipsed conformation, that repulsion is at a maximum, making it the less stable conformation. Eclipsed conformations possess torsional strain, and staggered conformations do not.