Chapter 4, Problem 73P

Haloethanes $\left({\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{X, X}=\text{Cl, Br, I}\right)$ have similar barriers to rotation $\left(\text{13}\text{.4-15}\text{.5 kJ/mol}\right)$ despite the fact that the size of the halogen increases, $\text{Cl}\to \text{Br}\to \text{I}$ . Offer an explanation.