>>7621872so there are several things to consider
alkyl groups are electron donating. Longer alkyl groups compound this effect. Ethyl of more electron donating than methyl, therefore the OH bond in ethyl is less polar than the OH in methyl, reducing the capacity of ethyl to H-bond slightly. (pKa methyl 15.5, ethyl 15.9)
The slight difference in polarity and h-bonding results in methanol having a bigger dielectric constant (which is a measure of polarity but not h-bonding) than ethanol.
Ethanol does have a larger surface area though, which means it has a greater capacity for london dispersion than methanol. This contributes a little but not enough to make up for the difference in polarity
Overall, methanol actually has higher intermolecular forces than ethanol. But since ethanol is heavier than methanol, ethanol has a higher BP and lower vapor pressure.
Unfortunately, for molecules that vary significantly in weight, BP is just not a good indicator of intermolecular forces. Just look at benzene, it has a higher BP than ethanol, but much weaker intermolecular forces.
