Chapter 4, Problem 4.30P

Interpretation Introduction

Interpretation:

The given conformations are to be ranked in the order from least to most stable.

Concept introduction:

Steric strain is the increase in energy of a conformer that results from electron repulsion between atoms or groups of atoms that are not directly bonded together but occupy the same space. In anti-conformation, bulky groups are ${180}^0$ apart in Newman projection. In Gauche conformation, bulky groups are ${60}^0$ apart, while in eclipsed conformation, bulky groups are in the closest proximity with torsional angle $0^0$. In the Newman projection, the conformations in which the substituents that are eclipsed to each other contribute the most steric strain to the molecule and are least stable. The conformations in which the substituents that are gauche to each other contribute steric strain to the molecule and are less stable. The conformations in which the substituents that are anti to each other do not contribute steric strain to the molecule and are most stable. Thus, the stability order for conformations is anti > gauche > eclipsed.