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Physical and Bond Properties

The polarity and linearity of the nitrile function add for extra intermolecular cohesion that makes nitrile boiling points higher than those of the corresponding alkanes of similar molecular weight.

Plot of boiling points against molecular weight for alkanes, esters, acyl halides, acids, amides and nitriles: nitriles boil at temperatures close to those of acids — Nitriles (stars) boil well above alkanes and esters of similar molecular weight, close to carboxylic acids. The linear and very polar C≡N group (dipole moment ≈ 3.9 D) holds the molecules together through strong dipole-dipole interactions, even though it does not form hydrogen bonds between them.

Similarly to an alkyne, the three atoms involved in the function C–C≡N are linear.

Model of acetonitrile with its bond lengths: C–H 1.09 Å, C–C 1.46 Å and C≡N 1.18 Å