Question

Butane and 2-methylpropane, whose space-filling models are shown, are both nonpolar and have the same molecular formula. Why does butane have the higher boiling point (-0.5 ∘C compared to -11.7 ∘C ).

Answer 1

In general straight chain alkanes are larger boiling points than branched chain alkanes, because straight chain molecules can also lie closer together - these attractions are at their most effective if the molecules are really close.

here butane has higer boiling point thant methyl propane

because the dispersion forces are greater. The butane molecules are longer (and so set up bigger temporary dipoles) and can lie closer together than the shorter, 2-methylpropane molecules