A Matrix Isolation and Ab Initio Study on C2H6…HCN Complex: an Unusual Example of Hydrogen Bonding

ABSTRACT Hydrogen bonding between saturated alkanes and HX (X is an electronegative fragment) represents a unique type of interaction of this kind. In this work we report a first experimental and ab initio study on HCN…C2H6 complex using FTIR matrix isolation spectroscopy and MP2/CBS calculations. According to theoretical results, three forms of HCN…C2H6 are possible: two with C(HCN)…C1(C2H6) and H(HCN)…C2(C2H6); C(HCN)…C1(C2H6) and N(HCN)…C2(C2H6) contacts and hydrogen-bonded H(HCN)…C(C2H6) axial symmetry structure (the interaction energies are 0.85, 0.79 and 0.77 kcal/mol respectively). Nevertheless, only the last structure is stabilized upon experimental conditions. The hydrogen-bonded complex is spectroscopically characterized by blue shifts of HCN bending (+9.4 cm−1) and CH3 rocking (+9.0 and +11.3 cm−1) and red shifts of H−CN stretching (−24.9 and −20.1 cm−1) and CH3 symmetry stretching (−4.7 cm-1) vibrations. The experiment with deuterated HCN proves this assignment. The obtained results are in good agreement with the previous rotational spectroscopy study.