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IR Intensities (ir + intensity)
Selected AbstractsChiral discrimination in hydrogen-bonded complexes of 2-methylol oxirane with hydrogen peroxideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Guiqiu Zhang Abstract A systematic quantum chemical study reveals the effects of chirality on the intermolecular interactions between two chiral molecules bound by hydrogen bonds. The methods used are second-order Møller,Plesset perturbation theory (MP2) with the 6-311++g(d,p) basis set. Complexes via the OH···O hydrogen bond formed between the chiral 2-methylol oxirane (S) and chiral HOOH (P and M) molecules have been investigated, which lead to four diastereomeric complexes. The nomenclature of the complexes used in this article is enantiomeric configuration sign corresponding to English letters. Such as: sm, sp. The relative positions of the methylol group and the hydrogen peroxide are designated as syn (same side) and anti (opposite side). The largest chirodiastaltic energy was ,Echir = ,1.329 kcal mol,1 [9% of the counterpoise correct average binding energy De(corr)] between the sm-syn and sp-anti in favor of sm-syn. The largest diastereofacial energy was ,1.428 kcal mol,1 between sm-syn and sm-anti in favor of sm-syn. To take into account solvents effect, the polarizable continuum model (PCM) method has been used to evaluate the chirodiastaltic energies, and diastereofacial energies of the 2-methylol oxirane···HOOH complexes. The chiral 2,3-dimethylol oxirane (S, S) is C2 symmetry which offers two identical faces. Hence, the chirodiastaltic energy is identical to the diastereomeric energy, and is ,Echir = 0.563 kcal mol,1 or 5.3% of the De(corr) in favor of s,s-p. The optimized structures, interaction energies, and chirodiastaltic energies for various isomers were estimated. The harmonic frequencies, IR intensities, rotational constants, and dipole moments were also reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Density functional study of HO(H2O)n (n = 1,3) clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005Xiu-Li Dong Abstract The hydrogen bonding complexes HO(H2O)n (n = 1,3) were completely investigated in the present study using DFT and MP2 methods at varied basis set levels from 6-31++G(d,p) to 6-311++G(2d,2p). For n = 1 two, for n = 2 two, and for n = 3 five reasonable geometries are considered. The optimized geometric parameters and interaction energies for various complexes at different levels are estimated. The infrared spectrum frequencies and IR intensities of the most stable structures are reported. Finally, thermochemistry studies are also carried out. The results indicate that the formation and the number of hydrogen bonding have played an important role in the structures and relative stabilities of different complexes. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Spectroscopic investigations and computational study of 2-[acetyl(4-bromophenyl)carbamoyl]-4-chlorophenyl acetateJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2010C. Yohannan Panicker Abstract The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 2-[acetyl(4-bromophenyl)carbamoyl]-4-chlorophenyl acetate were studied. The vibrational wavenumbers were examined theoretically using the Gaussian03 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution (PED) calculations. The simultaneous Raman and infrared (IR) activations of the CO stretching mode in the carbamoyl moiety show a charge transfer interaction through a ,-conjugated path. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of the CO bond and increases the double bond character of the CN bonds. The first hyperpolarizability and predicted IR intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar structures, which makes this compound an attractive object for future studies of nonlinear optics. Optimized geometrical parameters of the compound are in agreement with similar reported structures. Copyright © 2009 John Wiley & Sons, Ltd. [source] Density functional and vibrational spectroscopic analysis of ,-caroteneJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2003S. Schlücker Abstract We report a computational study on the structural, energetic and vibrational spectroscopic characteristics of ,-carotene employing density functional theory (DFT). The optimized geometry and the complete vibrational spectrum calculated at the BPW91/6,31G* level, including infrared (IR) intensities and Raman activities, are presented. The centrosymmetric structure of ,-carotene is verified both theoretically and experimentally, by identifying a stable calculated structure with Ci symmetry and the mutually exclusive occurrence of bands in the experimental Fourier transform IR and Raman spectrum, respectively. The calculated vibrational spectra reflect the major characteristic features observed experimentally. Differences in the calculated IR intensities and Raman activities for a few dominant modes of two ,-carotene configuration isomers, the all- trans and the natural abundant (C6,C7) s- cis form, are explained qualitatively by the corresponding eigenvectors. At the level of theory employed, s- cis -,-carotene was found to be 8.8 kJ mol,1 more stable than the all- trans form. Calculations on ,-carotene model systems were performed to separate electronic from steric contributions. The higher stability of s- cis -,-carotene is explained by an energetically favored ,-ionone ring conformation, compensating for its shorter conjugation length in comparison with the all- trans form. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characteristic Raman and IR bands of 3,3,-benzylidenebis(4-hydroxycoumarin) and its La(III), Ce(III) and Nd(III) complexesJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2006N. Trendafilova Abstract In the present paper we perform a detailed vibrational study of 3,3,-benzylidenebis(4-hydroxycoumarin) (phenyldicoumarol, PhDC) based on both experimental (IR and Raman) and calculated (DFT) vibrational spectra. To help the assignment of the PhDC vibrational modes, the vibrational spectrum of the monomeric building block, 4-hydroxycoumarin (4-HC), was also considered. The PhDC and 4-HC vibrational spectra were calculated and assigned at the B3LYP/6-31G* optimized geometries. The vibrational spectra of the La(III), Ce(III) and Nd(III) complexes with PhDC are discussed in a comparative study with the vibrational spectrum of the free PhDC ligand. The ,(CCH)ip, ,(CCH)op and ,(COH)ip vibrational modes as well as in-plane phenyl- and in-plane coumarin rings deformations were observed as strong bands in the Raman spectrum of PhDC and can be considered as a characteristic for the compound. Because of the very low IR intensity, these modes were not detected in the IR spectrum. Informative ligand vibrational modes were selected and their behaviors in the Ln(III) complexes were further studied to suggest the type of the PhDC binding mode to Ln(III) ions. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||