Isocyanides Versus Nitriles: Divergent Hydrogen Bonding Behavior Driven by the Balance Between Dispersive and Electrostatic Forces

Isocyanides as hydrogen-bond acceptors are characterized using jet-cooled Fourier transform infrared spectroscopy for the first time. The hydrogen-bonded structures of tert-butyl isocyanide (t-BuNC) and its constitutional isomer pivalonitrile (t-BuCN) with a single H₂O or tert-butyl alcohol (t-BuOH) molecule are analyzed. The most stable monohydrate structures differ markedly: t-BuNC adopts a classical σ-type hydrogen bond, whereas t-BuCN favors a dispersion-stabilized orthogonal π-type arrangement. Substitution of H₂O with the more polarizable t-BuOH enhances dispersion interaction between the molecules and drives both complexes toward π-type binding motifs. These findings highlight the balance between dispersive and electrostatic interactions in governing noncovalent binding preferences.