Arrange the given alkanes in increasing order of their boiling points. (A) 2, 2-dimethylpropane (B) 2-methylbutane (C) n -pentane (D) n -butane

Step-by-step solution

The boiling point of alkanes increases with an increase in molecular mass due to stronger van der Waals forces. Since n -butane (D) has four carbon atoms while the others have five, it has the lowest boiling point. For isomeric alkanes, the boiling point decreases with an increase in branching. Branching makes the molecule more spherical, which decreases the surface area of contact and weakens the intermolecular van der Waals forces. Among the isomers of pentane, n -pentane (C) is unbranched and has the highest sur