Vibrational spectra, ab initio/DFT electronic structure calculations, and normal coordinate analysis of 2-bromo-5-fluorobenzaldehyde

Tom Sundius, C.S. Hiremath

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Sammanfattning

FT-IR (4000–400cm−1) and FT-Raman (3500–50cm−1) spectral measurements of solid samples of 2-
bromo-5-fluorobenzaldehyde (BFB) have been done. Ab initio (RHF/6-311G*) and DFT (B3LY/6-311G*
and B3PW91/6-311G*) calculations have been performed giving energies, optimized structures, harmonic
vibrational frequencies, depolarization ratios, infrared intensities, Raman activities and atomic
displacements. Furthermore force field calculations have been performed by normal coordinate analysis.
Force field calculations showed that several normal modes are mixed in terms of the internal coordinates.
A complete assignment of the observed spectra, based on spectral correlations, electronic structure and
normal coordinate analysis, has been proposed. Optimization leads to CS symmetry with O-trans and Ocis
isomers, with respect to aldehydic oxygen and bromine, with O-trans-isomer as the low energy stable
form. The energy difference between the two isomers is 2.95084 kcal/mol. The results of the calculations
have been used to simulate IR and Raman spectra for BFB that showed excellent agreement with the
observed spectra. The SQM method, which implies multiple scaling of the ab initio and DFT force fields
has been shown superior to the uniform scaling approach.
Originalspråkengelska
TidskriftSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Volym74
Nummer5
Sidor (från-till)1260-1267
Antal sidor8
ISSN1386-1425
DOI
StatusPublicerad - dec. 2009
MoE-publikationstypA1 Tidskriftsartikel-refererad

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