Compare alcohols and ethers with the same molecular formula

Alcohols and ethers can be functional isomers. For example: $\text{C}_2\text{H}_6\text{O}:\quad \text{ethanol and dimethyl ether}$

What determines volatility?

A substance is more volatile if it has weaker intermolecular forces, because then it escapes more easily into the vapour phase.

Intermolecular forces in alcohols

Alcohols contain the $-OH$ group. Because hydrogen is directly attached to highly electronegative oxygen, alcohol molecules show intermolecular hydrogen bonding: $\text{R-OH} \cdots \text{HO-R}$

This strong attraction increases:

• boiling point
• association between molecules
• decreases volatility

Intermolecular forces in ethers

Ethers have the structure $\text{R-O-R'}$. They do not have an $O-H$ bond, so ether molecules cannot form intermolecular hydrogen bonding among themselves.

They mainly have:

• dipole-dipole interactions
• van der Waals forces

These are weaker than hydrogen bonding in alcohols.

Evaluate the options

• A: alcohols having resonance structures
  False. Ordinary alcohols do not show resonance responsible for this effect.

• B: inter-molecular hydrogen bonding in ethers
  False. Ethers do not show intermolecular hydrogen bonding with themselves because they lack an $O-H$ bond.

• C: inter-molecular hydrogen bonding in alcohols
  True. This is the correct reason alcohols are less volatile than corresponding ethers.

• D: dipole characters of ethers
  Not the main reason. Ethers are polar, but the key difference is the presence of hydrogen bonding in alcohols.

Final answer

Therefore, an ether is more volatile than an alcohol of the same molecular formula because alcohols have intermolecular hydrogen bonding.