Question

Ortho-chloro phenol is less polar than O-fluoro phenol. Why?

• A. Intra molecular H-bonding
• B. Inter molecular Hydrogen bonding
• C. Size of Cl as compared to size of F
• D. Cl is a gas

Answer 1

Answer: (A), (C)

Size of Cl as compared to size of F

The angle between the substituents, $-OH$ and $-Cl$, $-OH$ and $-F$ should ideally be ${60}^{\circ }$. Since $Cl$ is much bigger than $F$, the angle between $-OH$ and $-Cl$ increases. This results in reduction of $cos\theta$ values used in calculation of net dipole moment.

This results in net dipole moment dropping to lower value.