An insight into CH···N hydrogen bond and stability of the complexes formed by trihalomethanes with ammonia and its monohalogenated derivatives

Abstract

A theoretical study of the CH···N hydrogen bond in the interactions of trihalomethanes CHX 3 (X = F, Cl, Br) with ammonia and its halogen derivatives NH 2 Y (Y = F, Cl, Br) has been carried out thoroughly. The complexes are quite stable, and their stability increases in going from CHF 3 to CHCl 3 then to CHBr 3 when Y keeps unchanged. With the same CHX 3 proton donor, enhancement of the gas phase basicity of NH 2 Y strengthens stability of the CHX 3 ···NH 2 Y complex. The CH···N hydrogen bond strength is directly proportional to the increase of proton affinity (PA) at N site of NH 2 Y and the decrease of deprotonation enthalpy (DPE) of CH bond in CHX 3 . The CHF 3 primarily appears to favor blue shift while the red‐shift is referred to the CHBr 3 . The blue‐ or red‐shift of CHCl 3 strongly depends on PA at N site of NH 2 Y. We suggest the ratio of DPE/PA as a factor to predict which type of hydrogen bond is observed upon complexation. The SAPT2+ results show that all CH···N interactions in the complexes are electrostatically driven regardless of the type of hydrogen bond, between 48% and 61% of the total attractive energy, and partly contributed by both induction and dispersion energies.