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Vibrational spectrum, conformational stability, barriers to internal rotation, r 0 structural parameters and ab initio calculations of bromomethyl methyl ether
Author(s) -
van der Veken B. J.,
Guirgis G. A.,
Liu Jian,
Durig J. R.
Publication year - 1992
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250230405
Subject(s) - chemistry , raman spectroscopy , ab initio , conformational isomerism , deuterium , ab initio quantum chemistry methods , basis set , excited state , overtone , kinetic isotope effect , infrared , spectral line , molecule , computational chemistry , analytical chemistry (journal) , density functional theory , atomic physics , physics , organic chemistry , astronomy , chromatography , optics
The Raman and far‐infrared spectra at a resolution of 0.10 cm −1 of gaseous bromomethyl methyl ether, BrCH 2 OCH 3 , and three of its deuterium isotopes, d 2 , d 3 and d 5 , were recorded in the 350‐50 cm −1 region. The fundamental asymmetric torsional and methyl torsional modes for the d 0 molecule are extensively mixed and were observed at 176 and 130 cm −1 , respectively, for the stable gauche conformer with each mode having excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one‐dimensional model the barrier to internal rotation of the methyl moiety is determined to be 549 ± 8 cm −1 (1.57 ± 0.02 kcal mol −1 ). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500–50 cm −1 ) spectra of the gas and solid and Raman (3200–10 cm −1 ) spectra of the gas, liquid and solid is proposed. All of these data are compared with the corresponding quantities obtained from ab initio Hartree‐Fock gradient calculations employing the STO‐3G* basis set. Additionally, complete r 0 geometries were determined from the combined previously reported microwave data and CH distances determined from infrared studies along with carbon—hydrogen angles transferred from the corresponding chloride. The heavy atom structural parameters (distance in Å, angles in degrees) are r (C 1 Br) = 1.996 ± 0.005; r (C 1 O)=1.359 ± 0.005; r (C 2 O) = 1.433 ± BrCO = 113.7 ± 0.3; ∢ C 1 OC 2 = 113.5 ± 0.3 and dih BrC 1 OC 2 = 70.9 ± 0.3. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.