An IR spectroscopic investigation of blue shifting C–H⋯Cl hydrogen bonds in room temperature solution: Homomeric and mixed dimers of CHCl3 and CH2Cl2

Abstract

CH···Cl H-bonded homomeric and mixed dimers of CHCl3 and CH2Cl2 have been studied in room temperature CCl4 solution by observing spectral shift of νC−H fundamental transitions using IR spectroscopy. νC−H bands were found to show blue shift by 1.1 to 3.3 cm−1 upon CH···Cl H-bond formation in all the studied dimers. The findings were reinforced by observing νC−D spectral shifts for the corresponding dimers of the deuterated compounds, i.e., CDCl3 and CD2Cl2. νC−D bands also showed only blue shift within the range of 0.2 to 4.1 cm−1. All the experiments have been performed in another nonpolar solvent (C2Cl4) and the results were in close agreement with each other. Quantum chemical calculations predict multiple stable conformers for each of the dimers studied. In all the cases, the most stable conformers were solely C‒H···Cl H-bonded, confirming the observed νC−H spectral shifts to be brought about by intermolecular C‒H···Cl H-bond formation.