Vibrational spectra and conformational behavior of dicyclopropylmethane

Raman spectra of the condensed phases of dicyclopropylmethane have been recorded. In addition, i.r. spectra of this compound have been obtained for all three phases. From the appearance of spectral doublets in the liquid phase Raman (and i.r.) spectra, one member of each of which vanishes upon crystallization, it has been concluded that, in the liquid state, DCPM exists as an equilibrium mixture of at least two conformers. Based upon the spectral results for DCPM, and upon the conformational preferences of a number of related molecules, it has been concluded that these two conformers are the C₂ and C_sgauche/gauche rotational isomers, with the C₂ form being the one which remains in the solid phase. From a variable temperature study of liquid phase Raman peaks, it has been determined that the C₂ conformer of DCPM is more stable than the C_s conformer by 0.93 ± 0.10 kcal/mole. In addition, it appears that the C₂ rotamer of DCPM also predominates in the gaseous phase. Tentative assignments of the major spectral bands of DCPM have also been proposed.     

Vibrational spectra and conformational behavior of benzyl fluoride

Infrared and Raman spectra have been obtained for benzyl fluoride and a vibrational assignment has been made. The spectra indicate the presence of a large number of conformers that differ only in the orientation of the C-F bond, as a result of free or nearly free internal rotation.     

Vibrational spectra and conformational equilibrium of 1,1-dichloro-1-nitrosoethane and its deuterium analog

Conformational equilibrium has been detected in 1,1-dichloro-1-nitrosoethane, and the structures of the conformers have been determined. H/D isotope exchange has been used in assigning and calculating the normal vibrations.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2536–2540, November, 1989.     

Vibrational and rotational spectra and conformational behavior of (chloromethyl)thiirane

Infrared and Raman spectra of liquid and solid (chloromethyl)thiirane (3-chloropropylene sulfide), along with the infrared and microwave spectra of the vapor, have been recorded. The vibrational spectra are consistent with the existence of at least two conformations. Unlike the situation found for related molecules, the gauche-2 conformation of (chloromethyl)thiirane appears to be the most stable in all three phases. Variable temperature studies of the Raman spectra of the liquid allowed an enthalpy difference of 0.44 kcal mol⁻¹ between the gauche-1 and gauche-2 conformers to be calculated. The temperature dependence of certain Raman lines and the results of solution studies (infrared and Raman) suggest that a small amount of a third conformer (cis) might exist in the fluid phases. These experimental conclusions are supported by semi-empirical calculations (using the AM1 Hamiltonian) which suggest that all three conformers should be stable in the order: gauche-2 >gauche-1 >cis. In the microwave spectrum, the observed conformer has been experimentally determined to be the gauche-1 form with the rotational constants (in MHz): A = 7596.584, B = 1706.588, and C = 1476.982. The nuclear quadrupole constant η κ_aa_ has been determined to be −40.01 ± 0.38 MHz. The structure and conformations of (chloromethyl)thiirane are compared with related three-membered ring compounds.     

Vibrational spectra of cis-stilbene and 1,1-diphenylethene

Raman and IR spectra of the named compounds have been measured as liquids at room temperature and as solids at low temperature. Some bands are shown to arise from atomic displacements essentially localised on the weakly interacting phenyl groups; symmetric and anti-symmetric combinations of these “phenyl modes” are almost degenerate and become appreciably mixed in some cases leading to anomalous values for their depolarisation ratios. Other modes, largely involving the ethylenic group, are identified and provide information concerning the molecular conformation in the liquid; both molecules have C₂ molecular symmetry. The low-temperature spectra are sharp and contain information about the crystal structures.     

Vibrational spectra of trans-1,1-dihalo-2,3-dimethylcyclopropanes

The infrared spectra of trans-1,1-dichloro-2,3-dimethylcyclopropane and trans-1,1-dibromo-2,3-dimethylcyclopropane as liquids and polycrystalline solids have been measured. The gas-phase infrared spectrum of trans-1,1-dichloro-2,3-dimethylcyclopropane was also recorded from 4000 to 400 cm⁻¹. Raman spectra of the two compounds in the liquid phase have been obtained as well. An assignment of the vibrational frequencies has been proposed and discussed. A large number of fundamentals of the parent hydrocarbon are essentially unaffected by halogen substitution. Group frequencies like the ring pulsation and ring deformation modes are slightly, but characteristically shifted by halogen substitution. There is no indication of substantial steric crowding in these molecules.     

Vibrational spectra and conformational analysis of 1,3-dithia-5,6-benzocycloheptenes

The equilibrium between the chair and boat forms of 1,3-dithia-5,6-benzocycloheptene and its 2-Me, t-Bu, and Ph derivatives has been established by Raman and IR spectroscopy, and their spectroscopic characteristics have been revealed. In liquids the chair forms of 1,3-dithia(or dioxa)-5,6-benzocycloheptenes have C_s symmetry for the ring, and the twist forms of the seven-membered acetals have C₂ symmetry.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2014–2019, September, 1989.     

Vibrational spectra and the conformational composition of β-chloro- and β-bromophenetoles

Conclusions According to the data from vibrational spectrospyco, chloro- and bromophenetole in the crystalline state remain in the gauche orientation of the C-O and C-Hal bonds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1515–1518, July, 1986.     

Vibrational spectra and conformational isomerism of calixarene building blocks: 2-benzylphenol

The conformations and vibrational spectra of 2-benzylphenol have been analysed within the framework of scaled quantum mechanics. It is shown that the solid-state conformation of the 2-benzylphenol molecule corresponds to one of four potential energy minima predicted by non-empirical quantum chemical calculations for the isolated molecule. In the molten state and in diluted CCl4 solutions of the title compound this conformer coexists with another two spectroscopically detected conformations. The presence of several conformers gives rise to the observation of the corresponding number of vsCH2 and vasCH2 bands in the IR spectra, thus providing experimental evidence of the conformational sensitivity of the vCH2 frequencies. It is shown that vCH2 wavenumbers of different kinds of molecules, containing diphenylmethane fragments, are determined by the dihedral angles between the planes of the aromatic rings and the plane of the connecting methylene bridges, except for the case of short intramolecular contacts with the participation of the methylene protons.     

Vibrational spectra and conformational isomerism of 2-phenoxy-5,6-benz-1,3,2-dioxaphosphepins

Conclusions Using vibrational spectroscopy methods in different aggregate states and solutions with variation of the polarity of the medium, we have studied 2-phenoxy-5,6-benz-1,3,2-dioxaphosphepin and its oxo, thio, and seleno analogs. In the liquid and solutions, they exist as a conformational equilibrium of three forms: two chair forms, differing in the orientation of the phenoxyl radical, and a twist form. The population of the twist form is no more than 25%. The content of the chair conformers is determined by the solvent. In the crystal, all the compounds have the chair form with axial phenoxyl group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 844–849, April, 1989.     

Vibrational spectra,conformational equilibria,ab initio calculations and vibrational assignments of ethylmethylfluorosilane

The infrared spectra of ethylmethylfluorosilane (CH₃SiHFCH₂CH₃) have been recorded as a vapour, liquid and solid at 78 K in the 4000–50 cm⁻¹ range and isolated in an argon matrix at ca. 5 K. Infrared spectra of two different solid phases were obtained after annealing to temperatures of 120 and 130 K, and recooling to 78 K. Although the IR spectra were quite similar in the MIR region, certain differences were noted in the FIR region below 400 cm⁻¹. The most stable conformer MeMe was present after annealing to 130 K, but three bands belonging to MeH were detected after annealing to 120 K. Various infrared bands changed intensity when the argon matrix was annealed to temperatures between 20 and 35 K, and some of these were related to changes in the conformational abundance.Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, various bands changed in intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer MeMe. From various bands assigned to the three conformers, the conformational enthalpy difference ΔH from MeMe to the intermediate energy conformer MeH was found to be 0.5 kJ mol⁻¹ and to the highest conformer MeF was 0.7 kJ mol⁻¹. At ambient temperature this leads to 39% MeMe, 32% MeH and 29% of the MeF conformer in the liquid.Ab initio calculations in the RHF, MP2, DFT approximations and very accurate G2 calculations were carried out. With one exception, the MeMe conformer had the lowest enthalpy in all these calculations, the MeH had the intermediate and the MeF the highest enthalpy, and the calculations were in good agreement with the measurements.     

Vibrational analysis of 1,1-dichlorobutane

IR and Raman spectra have been obtained for 1,1-dichlorobutane and interpreted with the aid of normal coordinate calculations. It is concluded that this compound exists in three conformations in the liquid and glassy solid states but crystallizes only in the conformer that has all four carbons coplanar and both chlorines out of that plane (C_s symmetry).     

Vibrational spectra and structure of cis- and trans-1,2- dimethoxyethylenes

The vapor, liquid and CCl₄ solution infrared spectra of cis- and trans-1,2-dimethoxyethylene were recorded in the region 250–4000 cm^?1. The laser-Raman spectra were obtained in the liquid state only. The vibrational spectra show that at least two rotational isomers exist for each molecule. Further, the spectra indicate that for both the cis- and trans molecules, one of the rotational isomers has at least one planar conformer. Some vibrational assignments are made for the observed infrared and Raman bands of the cis- and trans- 1,2-dimethoxyethylenes.     

Vibrational spectra of hexamethylcyclodisilazane

The synthesis and ring cleavage reactions of 2-alkyl-2-trimethylsilylmethyl-1.3-dithianes are described. The cleavage lead to 2-alkylthio-1-vinylsilanes and, via silicon migration, to 2-[3-alkylthio-3-(trimethylsilyl)propylthio]-1-alkenes.     

Vibrational spectra of mesitylene

Conclusions The Raman spectra of liquid mesitylene and the IR spectra (4000-100 cm^–1) of liquid and gaseous mesitylene were studied. An assignment of the frequencies according to the symmetry and the form of the vibrations is proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2265–2270, October, 1982.     

Vibrational spectra of diethylsulfoxide

FT IR and Raman spectroscopic studies of pure diethylsulfoxide (DESO) in the liquid and in the solid states and its solutions in various solvents have been performed. Analysis of SO- and CH-stretching regions in a wide range of concentration shows that the bands may be fitted satisfactorily by considering seven components. In addition, fundamental frequencies have been assigned using ab initio calculations at the RHF/3-21G* levels. The results obtained confirm a viewpoint on a self-associative structure of DESO, and support the hypothesis of the existence of different types of intermolecular associates including both dipole-dipole and hydrogen bonding mechanisms.