Q.Between 1-chlorobutane (a straight-chain haloalkane) and 2-chloro-2-methylpropane ($\text{tert}$-butyl chloride, a highly branched isomer of the same molecular formula), which has the higher boiling point? Explain using molecular shape.

1-Chlorobutane is a straight, extended chain, while 2-chloro-2-methylpropane (tert-butyl chloride) is compact and nearly spherical, with three methyl groups branching off a central carbon. A straight-chain molecule can pack closer to, and make more extended surface contact with, its neighbours, maximising the cumulative London dispersion attraction between molecules; a compact, spherical molecule of the same molecular formula presents comparatively little surface area for such contact. Since both isomers have the identical molecular formula ($\text{C}_4\text{H}_9\text{Cl}$) and hence identical mass and an identical, single C--Cl bond dipole, the difference in boiling point …

Compare only isomers with the same molecular formula on the branching-vs-shape argument -- it isolates the effect of sh …

Assuming the more substituted (tertiary) halide must have the higher boiling point by analogy with, e.g., carbocation stability -- boiling point t …