[Amyco]

Ok, so...

Why do the differences in boiling points between alcohols and alkanes get less as the number of carbon atoms in a chain increases??     For example, Methane 90C Methanol 338C - difference 248C, then Heptane 342C Heptanol 449 - difference 107C.

I know that alcohols have a higher boiling point generally due to their O-H group but why does the difference decrease if each gains the same number of carbon atoms? 

Any advice appreciated.

[Yggdrasil]

Methane boils at 90^oC?  Methane is a gas at RT.

To answer your question, as the size of the molecules increase, dispersion forces become more significant.  Since dispersion forces between the linear alkanes and alcohols are similar, you will see their boiling points begin to converge.

[Amyco]

Whoops, I meant K not C! 

Thanks for your answer, I understand it now