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Gas‐Phase Infrared Spectroscopy of Substituted Cyanobutadiynes: Roles of the Bromine Atom and Methyl Group as Substituents
Author(s) -
MonteroCampillo M. Merced,
Mó Otilia,
Yáñez Manuel,
Benidar Abdessamad,
Rouxel Cédric,
Kerisit Nicolas,
Trolez Yann,
Guillemin JeanClaude
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201501153
Subject(s) - chemistry , substituent , bromine , infrared spectroscopy , density functional theory , infrared , derivative (finance) , atom (system on chip) , methyl group , ab initio quantum chemistry methods , spectroscopy , crystallography , spectral line , ab initio , photochemistry , computational chemistry , group (periodic table) , stereochemistry , molecule , physics , organic chemistry , quantum mechanics , astronomy , computer science , financial economics , optics , economics , embedded system
Abstract The IR spectra of 5‐bromo‐2,4‐pentadiynenitrile (Br−C≡C−C≡C−CN) and 2,4‐hexadiynenitrile (CH 3 −C≡C−C≡C−CN), a compound of interstellar interest, have been recorded within the 4000–500 cm −1 spectral region and calculated by means of high‐level ab initio and density functional calculations. Although the calculated structures of both compounds are rather similar, there are very subtle differences, mainly in the strength of the C≡C bond not directly bound to the substituent. These subtle bonding differences are reflected in small, but not negligible, differences in the electron density at the corresponding bond critical points, and, more importantly, are reflected in the IR spectra. Indeed, the IR spectrum for the bromine derivative presents two well‐differentiated strong bands around 2250 cm −1 , whereas for the methyl derivative both absorptions coalesce in a single band. These bands correspond in both cases to the coupling between C≡C and C≡N stretching displacements. A third, very weak, band also associated with C≡C and C≡N coupled stretches is observed for the bromine derivative, but not for the methyl one, owing to its extremely low intensity.