Arrange the following alcohols in order of increased boiling point and explain:?

Question

(CH3)3COH, CH3(CH2)4OH, (CH3)3CCH2OH, and
(CH3)CHCH2OH

Answer 1

The stronger the intemolecular forces, the more energy needed to break them, thus the higher boiling point.

All of them have only single bonds and only 1 -OH group. So the strength of the H-Bonds is similar in all cases and the difference in the boiling points will be determined by the difference in the dispersion forces (or van der Waals forces) between the hydrophobic parts of the alcohol.

These forces increase as the surface of the molecule increases. The more branched a molecules is, the smaller its surface (always talking about the same number of atoms) thus the weaker the intemolecular forces will be and the lower the boiling point. Also the fewer the atoms the smaller the overall surface. So (CH3)3COH will have the smallest boiling point since it is the smallest (4 carbon atoms instead of 5) and at the same time most branched of the molecules.

So the order is


(CH3)3COH < (CH3)3CCH2OH < (CH3)2CHCH2OH< CH3(CH2)4OH

I must admit I am not 100% that (CH3)3CCH2OH < (CH3)2CHCH2OH because although the latter is less branched it is smaller (4 instead of 5 C atoms).It's a tough call. Had to look for the actual values which are 113 C and 132 C respectively, so the order is correct.