Chapter 4, Problem 4.4YT

Interpretation Introduction

Interpretation:

Each of the unlabeled conformations as either eclipsed or staggered in Fig. 4-4 is to be labeled.

Concept introduction:

To understand the nature of a rotation about a given bond, we perform a conformational analysis, which is a plot of a molecule’s energy as a function of that bond’s dihedral angle. The energy values for various angles of rotation are relative to that of the lowest-energy conformation. Figure 4-4 depicts the conformational analysis of ethane (${\text{H}}_{\text{3}}{\text{C-CH}}_{\text{3}}$) about the $\text{C-C}$ bond. 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. Because all the hydrogen substituents are identical, these three conformations are indistinguishable. 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.