Issue 33, 2018

Hydrogen bond induced enhancement of Fermi resonances in N–H⋯N hydrogen bonded complexes of anilines

Abstract

The hydrogen-bonded complexes of aniline, 4-fluoroaniline and 4-ethynylaniline with ammonia, methylamine, dimethylamine, trimethylamine and triethylamine, were investigated using IR-UV double resonance spectroscopy. The formation of N–H⋯N hydrogen bonded complexes with anilines as donors and alkylamines as acceptors was inferred from the appearance of the spectra. Two bands appearing in the 3100–3400 cm−1 region were found to be originating from the Fermi resonance coupling between the hydrogen-bonded NH2 stretching and NH2 bend-overtone vibrations. A two-state de-perturbation analysis yields the zero-order (unperturbed) vibrational states and the coupling constant. An inverse correlation between the zero-order hydrogen-bonded NH2 stretching and NH2 bend-overtone was observed due to a switch in the relative contributions of hydrogen-bonded NH2 stretching and NH2 bend-overtone vibrations to the Fermi resonance bands. These results lead to the reassignment of the hydrogen-bonded N–H stretching frequencies of aniline complexes reported earlier. Furthermore, the stretch-bend Fermi-resonance coupling constant for the NH2 group is around 50 cm−1, which is independent of the nature of the parent donor molecule and the acceptor, and is intrinsic to the NH2 group.

Graphical abstract: Hydrogen bond induced enhancement of Fermi resonances in N–H⋯N hydrogen bonded complexes of anilines

Supplementary files

Article information

Article type
Paper
Submitted
01 شعبان 1439
Accepted
07 ذو القعدة 1439
First published
07 ذو القعدة 1439

Phys. Chem. Chem. Phys., 2018,20, 21557-21566

Hydrogen bond induced enhancement of Fermi resonances in N–H⋯N hydrogen bonded complexes of anilines

S. Mishra, J. Kuo and G. N. Patwari, Phys. Chem. Chem. Phys., 2018, 20, 21557 DOI: 10.1039/C8CP02448K

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