Chapter 4, Problem 4.36P

Interpretation Introduction

Interpretation:

The ring strain per ${\text{CH}}_{\text{2}}$ group and the total ring strain of cyclononane is to be calculated. Which compound has more ring strain, cyclononane or cycloheptane, is to be stated.

Concept introduction:

Ring strain is the type of instability that exists when bonds in a molecule form angles that are abnormal. Ring strain can also be defined as the increase in energy due to geometric constraints on the ring. For a given cycloalkane, the ring strains per ${\text{CH}}_{\text{2}}$ group can be calculated using heats of combustion values. Heat of combustion (${\text{ΔH}}^{\text{0}}$) is the energy given off in the form of heat during a combustion reaction. Any difference in the heat of combustion per ${\text{CH}}_{\text{2}}$ group for two cyclic alkanes reflects a difference in ring strain per ${\text{CH}}_{\text{2}}$ group. The total ring strain is obtained by multiplying the strain per ${\text{CH}}_{\text{2}}$ group by the number of ${\text{CH}}_{\text{2}}$ groups, (n). For cyclohexane, the ring strain per ${\text{CH}}_{\text{2}}$ group and the total ring strain is $\text{0 kJ/mol}$, hence it is used as a standard to compare the ring strains and the total ring strain for other cycloalkanes.