Q.Arrange the following in increasing order of their boiling point and give a reason for your ordering:

Step 1. (i) Among isomeric butanols, boiling point falls as branching/substitution at the carbinol carbon increases: the compact, highly-branched TERTIARY alcohol (2-methylpropan-2-ol) packs and hydrogen-bonds least effectively (lowest bp, about 82 C); the SECONDARY alcohol (butan-2-ol) is intermediate (about 100 C); the straight-chain PRIMARY alcohol (butan-1-ol) has the largest surface area for intermolecular hydrogen bonding and van der Waals contact (highest bp, about 118 C).

Step 2. So the increasing order is: 2-methylpropan-2-ol < butan-2-ol < butan-1-ol. …

Rank by the two governing factors in turn: branching (fewer effective H-bonds = lower bp) for isomeric monools, and -OH count (more H-bon …

• Assuming molar mass alone determines boiling point among close isomers -- here it is the DEGREE OF BRANCHING (part i) and the NUMBER of -OH groups (part ii) that dominate, not small mass differences. …