Question

The following data for isomeric four-carbon alcohols show that there is a decrease in boiling point with increasing substitution of the OH-bearing carbon. How might you account for this trend?

1-Butanol, bp 117.5 °C

2-Butanol, bp 99.5 °C

2-Methyl-2-propanol, bp 82.2 °C

Answer 1

Among the isomeric alcohols given, as the branching increeases the boiling point decrases.

All have same functional group, similar H- bonding.

The difference in boiling point canbe attributed to the difference in vanderwaals' forces.

The vander waals' forces /dispersion forces between the molecules depend on the surface area and symmetry of the molecule.

More branching , more symmetrical is the molecule, and lesser will be surface area.

So the higher the branching, lesser is surface area, less are the vanderwaals' attractions, that result in lower boiling ppoint.

Hence the trend in boiling point order.

the order of b.p is primary > secondary > tertairy alcohols