title: DFT studies on the structural and vibrational properties of polyenes.
abstract: Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C-C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon-carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C = C units with both ends substituted by tert-butyl groups. The corrected ν(C = C) and ν(C-C) wavenumbers for all-trans molecules were used to estimate the presence of 9 - 12 C = C units in all-trans polyene pigment in red coral.
authors.affiliation: Faculty of Chemistry, University of Opole, 48 Oleska Street, 45-052, Opole, Poland. teobaldk@gmail.com.
authors.forename: Teobald
authors.initials: T
authors.lastname: Kupka
authors.affiliation: Faculty of Chemistry, University of Opole, 48 Oleska Street, 45-052, Opole, Poland. abuczek@uni.opole.pl.
authors.forename: Aneta
authors.initials: A
authors.lastname: Buczek
authors.affiliation: Faculty of Chemistry, University of Opole, 48 Oleska Street, 45-052, Opole, Poland.
authors.forename: Małgorzata A
authors.initials: MA
authors.lastname: Broda
authors.affiliation: Faculty of Chemistry, University of Opole, 48 Oleska Street, 45-052, Opole, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Stachów
authors.affiliation: Faculty of Chemistry, University of Opole, 48 Oleska Street, 45-052, Opole, Poland.
authors.forename: Przemysław
authors.initials: P
authors.lastname: Tarnowski
mesh_terms: D005030:Ethylenes / Q000737:chemistry; D008958:Models, Molecular; D011090:Polyenes / Q000737:chemistry*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D014732:Vibration
chemical_list: D005030:Ethylenes; D011090:Polyenes; C036216:ethylene
keywords: All-cis polyenes; All-trans polyenes; C-C bond; C = C bond; DFT; IR and Raman spectroscopy