Weak hydrogen bonds between alkyl halides and amides: The microwave spectroscopic and theoretical study of the difluoromethane⋯formamide complex

Tao Lu; Juncheng Lei; Qian Gou; Gang Feng

doi:10.1016/j.saa.2020.118681

Weak hydrogen bonds between alkyl halides and amides: The microwave spectroscopic and theoretical study of the difluoromethane⋯formamide complex

Spectrochim Acta A Mol Biomol Spectrosc. 2020 Nov 5:241:118681. doi: 10.1016/j.saa.2020.118681. Epub 2020 Jul 2.

Authors

Tao Lu¹, Juncheng Lei¹, Qian Gou¹, Gang Feng²

Affiliations

¹ School of Chemistry and Chemical Engineering, Chongqing University, Daxuecheng South Rd. 55, 401331 Chongqing, China.
² School of Chemistry and Chemical Engineering, Chongqing University, Daxuecheng South Rd. 55, 401331 Chongqing, China. Electronic address: fengg@cqu.edu.cn.

PMID: 32653826
DOI: 10.1016/j.saa.2020.118681

Abstract

The pure rotational spectrum of the complex of difluoromethane with formamide was investigated by means of microwave spectroscopy supplemented with theoretical calculations. The hyperfine structure arising from the ¹⁴N nuclear quadrupole coupling effect was completely resolved. The most stable isomer that displays the C_s symmetry with the ∠HCH angle of difluoromethane being bisected by the ab-plane of formamide was detected. The two moieties in the detected isomer are connected via one N-H⋯F and one bifurcated CH₂⋯O weak hydrogen bonds confirmed by the non-covalent interaction plot and natural bond orbital analyses. The distances of the NH⋯F and CH₂⋯O interactions were determined to be 2.140(14) Å and 2.749(14) Å, respectively. The NH⋯F bond angle was determined to be 150.7°. Symmetry-adapted perturbation theory analysis indicates that the electrostatic component is the largest contributor to the total attractive interaction energy of the difluoromethane⋯formamide complex.

Keywords: Dissociation energy; Hydrogen bonds; N—H⋯F interaction; Quantum chemical calculations; Rotational spectroscopy; Weakly bound molecular complex.