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Infrared Intensities (infrared + intensity)
Selected AbstractsInfrared intensities of benzene derivatives as a measure of the substituent resonance effectJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2001Karel Palát Jr Abstract Infrared spectra of 39 benzene mono-derivatives were recorded in the region 1000,1800,cm,1 and the intensities of the bands ,16a and ,16b were determined by computer separation. The intensities correlated with the squared resonance substituent constants ,Ro as found by Katritzky and co-workers, but band separation does not represent any essential improvement compared with the earlier simpler technique. With substituents including an NH2 group, there is still an interference with the NH2 scissoring deformation band: in these cases deuteration is more effective than band separation. Several new constants ,Ro were determined spectroscopically for substituents of interest in pharmacology and these constants were also calculated by a quantum chemical model. The latter procedure seems to be most efficient and reasonably reliable for calculating new ,Ro constants; the only problem may be with the conformation in the case of axially unsymmetrical substituents. Copyright © 2001 John Wiley & Sons, Ltd. [source] Mechanisms and kinetics for preparing carbohydrazide by reacting dimethyl carbonate with hydrazine: A theoretical studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008Jianguo Zhang Abstract The mechanism and kinetic modeling for preparing carbohydrazide from dimethyl carbonate and hydrazine has been declared. The geometries of all the stationary points (reactants, intermediates, transition states, and products) are optimized by using the B3LYP method with the cc-pVDZ basis set, and the harmonic vibrational frequencies as well as infrared intensities are predicted with the same method. The minimum-energy paths are obtained by using the intrinsic reaction coordinate (IRC) theory at the B3LYP/cc-pVDZ level of theory with the step length 0.02 (amu)1/2·bohr. The rate constants are evaluated by using the TST, TST/Eckart, and RRKM (T)/Eckart methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] FT-Raman, FT-IR spectral and DFT studies on 6, 8-dichloroflavone and 6, 8-dibromoflavoneJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2010Yusuf Erdogdu Abstract In this study, experimental and theoretical vibrational spectral results of the molecular structures of 6,8-dichloroflavone (6,8-dcf) and 6,8-dibromoflavone (6,8-dbf) are presented. The FT-IR and FT-Raman spectra of the compounds have been recorded together between 4000 and 400 cm,1 and 3500,5 cm,1 regions, respectively. The molecular geometry and vibrational wavenumbers of 6,8-dcf and 6,8-dbf in their ground state have been calculated by using DFT/B3LYP functional, with 6-31 + + G(d,p) basis set used in calculations. All calculations were performed with Gaussian03 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities are also reported. Copyright © 2009 John Wiley & Sons, Ltd. [source] Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of dimethylsilylisocyanateJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2010Gamil A. Guirgis Abstract The Raman (3200-30 cm,1) and/or infrared spectra (3500 to 400 cm,1) of gaseous, liquid and solid dimethylsilylisocyanate, (CH3)2 Si(H)NCO, have been recorded. The MP2(full) calculations, employing a variety of basis sets with and without diffusion functions, have been used to predict the structural parameters, conformational stability, vibrational fundamental wavenumbers, Raman activities, depolarization values and infrared intensities to support the vibrational assignment. The low wavenumber Raman spectrum of the gas with a significant number of Q-branches for the SiNC(O) bend is consistent with an essentially linear SiNCO moiety. The ab initio calculations supported this conclusion as all possible orientations of the NCO moiety lead to nearly the same energy. This result is at variance with the conclusion from the electron diffraction study that the heavy atom skeleton was bent with an angle of 152(5)° with one stable cis conformer. It is believed that this reported angle difference from 180° is due to the shrinkage effect. The SiH distance of 1.486 Ĺ has been obtained from the isolated SiH stretching wavenumber. From the adjustment of the ab initio MP2(full)/6-311+G(d,p) predicted structural parameters, a proposed structure is reported, which is expected to give rotational constants within a few megahertz of the actual ones. These experimental and theoretical results are compared with the corresponding quantities of similar molecules. Copyright © 2009 John Wiley & Sons, Ltd. [source] Chirality of camphor derivatives by density functional theory,CHIRALITY, Issue 10 2006Hayato E. Morita Abstract Infrared (IR) and vibrational circular dichroism (VCD) spectra of chiral camphor, camphorquinone and camphor-10-sulfonic acid (CSA), known as standard compounds for electronic circular dichroism (ECD) spectroscopy, are measured and their vibrational frequencies, infrared intensities, and rotational strengths are calculated using density functional theory (DFT). The observed IR and VCD spectra of chiral camphor and camphorquinone in carbon tetrachloride solution are reproduced by the DFT calculations, but those of CSA are not. DFT calculations of hydration models, where an anionic CSA specifically binds a few water molecules, are carried out. The average of the simulated VCD spectra in the hydration models is more consistent with the observed spectra. In addition, the wavelengths and dipole and rotational strengths for chiral camphor, camphorquinone, anionic CSA, and the hydration models were calculated by time-dependent DFT. In the region of 280,300 nm, the calculated wavelengths of the ECD bands for chiral camphor and camphorquinone coincide with the observed wavelengths that have been reported, and the calculated wavelengths for the hydration models are closer to the observed wavelengths reported than are those calculated for chiral anionic CSA. Consequently, the analysis combined with VCD and ECD spectroscopy using DFT calculations can elucidate the chirality of optically active molecules, even in an aqueous solution. Chirality, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||