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

TL;DR

The paper shows how isocyanides and nitriles form different hydrogen bonds with water or alcohol, influenced by electrostatic and dispersive forces.

Contribution

First characterization of isocyanides as hydrogen-bond acceptors using jet-cooled infrared spectroscopy.

Findings

t-BuNC forms classical σ-type hydrogen bonds with H2O, while t-BuCN prefers dispersion-stabilized π-type arrangements.

Replacing H2O with t-BuOH enhances dispersion interactions, shifting both complexes toward π-type binding.

Hydrogen bonding preferences are governed by the balance between electrostatic and dispersive forces.

Abstract

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.

While isocyanides favor σ‐type hydrogen bonding, as illustrated by t‐BuNC···H2O (top), nitriles prefer π‐type hydrogen bonding, as illustrated by t‐BuCN···H2O (bottom). The σ‐type complex is characterized by a larger OH vibrational downshift due to more efficient charge transfer, whereas the π‐type complex is mainly stabilized by dispersion and thus exhibits a smaller OH vibrational downshift.© 2026 WILEY‐VCH GmbH

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