Vibrational spectrum and conformation of cyclopropyldichloroborane

The infrared (3500-40 cm^?1) and Raman spectra (3200-0 cm^?1) have been recorded for cyclopropyldichloroborane in both the gaseous and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values obtained. Only one conformation has been found in all three physical states and, on the basis of the polarized nature of the Raman band assigned as the BCl₂ antisymmetric stretch, this conformer has been identified as being the bisected structure with C_s molecular symmetry. A complete vibrational assignment is proposed based on Raman depolarization data, infrared gas phase band contours, and group frequencies. These results are compared with the corresponding data in other organoboranes.     

Infrared,Raman spectra and vibrational assignment of (PF2)2O

The IR spectra of gaseous and solid (PF₂)₂O has been recorded from 80 to 1200 cm^?1. The Raman spectra of gaseous, liquid and solid (PF₂)₂O have also been obtained (30–1000 cm^?1). The spectra of the fluid phases indicate the presence of at least two conformers. The spectrum of the solid phase can readily be interpreted on the basis of a single conformer possessing a symmetry lower than C_2v. A vibrational assignment is proposed for all normal modes except the PF₂ torsions. The results are compared with similar data of related compounds. There appear to be two molecules per primitive cell based upon the low-frequency Raman data.     

FTIR and Raman studies on benzimidazole

The FTIR and laser Raman spectra of benzimidazole have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming C_s point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.     

The vibrational spectra and conformational properties of liquid dimethyl oxalate

The infrared spectra of dimethyl oxalate and dimethyl oxalate-d₆ have been recorded in the liquid phase. These spectra are compared with both the infrared and Raman spectra recorded in solid phase. It is shown that dimethyl oxalate exists as a conformational equilibrium mixture in the liquid phase. The most stable conformer is that present exclusively in the crystal, the planar, cis-ester C_2h structure. The second conformer is probably one formed by rotation about the carbonyl carbon-oxygen bonds of the molecule.     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.     

Conformational analysis,barriers to internal rotation,vibrational assignment and ab initio calculations of chloroacetone

The infrared (3500-20 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra have been recorded for gaseous and solid chloroacetone (1-chloro-2-propanone), CH₂ClC(O)CH₃. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis that the molecule exists predominantly in a gauche conformation having a “near cis” structure of C₁ symmetry (dih ClCCO=142°C) in the vapor but for the liquid a second conformer having a trans structure (chlorine atom oriented trans to the methyl group) with C_s point group symmetry is present. From a study of the Raman spectrum of the liquid at variable temperatures, the trans conformation has been determined to be more stable than the gauche form by 1042±203 cm⁻¹ (2.98±0.6 kcal mol⁻¹ and is the only conformer present in the spectrum of the annealed solid. From ab initio calculations at the 3-21G* and 6-31G* basis set levels optimized geometries for both the gauche and trans conformers have been obtained and the potential surfaces governing internal rotation of the symmetric and asymmetric rotors have been obtained. The observed vibrational frequencies and assignments to the fundamental vibrations for both the gauche and trans conformers are compared to those calculated with the 3-21G* basis set. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

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).     

Observation of a phase transition in ThBr4 and ThCl4 single crystals by far-infrared and Raman spectroscopy study

At 4 K the visible and infrared absorption and emission spectra of U⁴⁺ in ThBr₄ and ThCl₄ single crystals are not very consistent with what is predicted by the selection rules for the room temperature structure. Thus we investigated Raman scattering in the temperature range 10–300 K to look for a structure change and obtain a better understanding of the spectroscopy of U⁴⁺ in ThBr₄ and ThCl₄. At room temperature, the observed Raman lines have been assigned on the basis of a D_4h factor group analysis. The study of the temperature dependence of the Raman spectra permitted us to discover phase transitions of ThBr₄ and ThCl₄ at 95 and 70 K, respectively. The splitting observed for the strongest E_g symmetry mode shows a lowering of the symmetry below the transition point. Powder X-ray diffraction at 77 K of hygroscopic ThBr₄ is being carried out to determine the low-temperature structure.     

Vibrational spectra and analyses of MFe(CO)4 (M = Cd,Hg)

The IR and Raman spectra of the compounds CdFe(CO)₄ and HgFe(CO)₄, are reported and assigned using C_2v, local symmetry around the iron atom; vibrational analyses of the spectra have also been carried out. The spectroscopic data obtained indicate that the compounds are probably polymers with a centre of symmetry and an octahedral configuration about the iron atom in accordance with X-ray structural results.     

The infrared and Raman spectra of pyromellitic dianhydride

The infrared and Raman spectra of solid state samples of pyromellitic dianhydride have been measured. The infrared—Raman mutual exclusion rule has been observed and the frequencies have been tentatively assigned on the basis of D_2h symmetry. The values of the CO and skeletal ring stretching frequencies have been interpreted in terms of a conjugated π-system.     

Laser Raman and infrared spectra of deuterated silylgermanes

The laser Raman and infrared spectra of deuterated silylgermanes have been recorded on a Cary model 82 grating spectrophotometer with an argon laser source and a Perkin—Elmer 983 double beam grating spectrophotometer, respectively. The spectra have been analysed on the basis of fundamental combinations and overtones and the frequencies have been assigned to various modes of vibration, assuming C_3υ point group symmetry. Furthermore, based on the force field for silylgermanes, the vibrational frequencies of isotopically substituted species have been calculated and the results are briefly discussed.     

Vibrational spectra,methyl torsional potential functions,internal rotational potential functions,and conformational properties of ethyl vinyl ether

The vibrational spectra of ethyl vinyl ether in both the fluid and solid states have been recorded from 20 to 3500 cm^?1. The 33 fundamental modes of vibration have been assigned. Three rotational isomers have been observed and their structures have been determined. The most stable conformer, s-cis/s-trans, is planar and of C_s symmetry. The two less stable rotamers, skew/s-trans and skew/gauche, are non-planar and of C_i molecular symmetry. The barrier to internal rotation of the methyl rotor has been determined for each conformation; these barriers are 3.43 kcal mol^?1 (s-cis/s-trans), 3.35 kcal mol^?1 (skew/s-trans) and 3.19 kcal mol^?1 (skew/gauche). A potential function for each of the two asymmetric internal rotations has been calculated and barriers to conformer interconversion have been determined. From the asymmetric potential function calculations, ΔH, the enthalpy difference between the conformers, has been determined. The s-cis/s-trans conformer is 1.87 kcal mol^?1 more stable than the skew/s-trans conformer; the skew/s-trans conformer is more stable than the skew/gauche conformer by 1.10 kcal mol^?1. The energetics of conformer interconversion and methyl internal rotation have been described in terms of molecular geometry and non-bonded interactions. These results are compared to those found in other alkyl vinyl and dialkyl ethers.     

Surface-enhanced Raman spectra of benzene and benzene-d6 on vapor-deposited sodium

Enhanced Raman spectra have been observed from small amounts of benzene and benzene-d₆ adsorbed on vapor-deposited sodium surfaces held at 15 K. Many lines were observed which can be assigned to normally Raman-active benzene fundamentals as well as some that are normally forbidden in D_6h symmetry.     

The vibrational spectra of N-Cl maleimide

The infrared spectra of N-Cl maleimide as a Nujol mull and dissolved in various solvents were recorded between 4000 and 30 cm^?1. Raman spectra of the crystalline solid and saturated solution in CH₃CN were recorded and semiquantitative polarization measurements were made.The fundamental frequencies have been tentatively assigned in terms of C_2V symmetry, based upon Raman polarization data and analogies with the spectra of maleimide and maleic anhydride. A force field was derived by initially transferring force constants from maleimide. After small iterations a satisfactory correspondance was achieved between the observed and calculated in-plane modes whereas larger discrepancies remained for some of the out-of-plane vibrations.     

Conformation and vibrational spectra of 1,5-hexadiyne (bipropargyl) and 1,5-hexadiyne-1,6-d2

The infrared spectra of 1,5-hexadiyne (bipropargyl) and 1,5-hexadiyne-1,6-d₂ as vapours, liquids, as solutes in various solvents and as crystalline solids at low temperatures and at high pressures have been recorded. Raman spectra were obtained for the liquids, including semiquantitative polarization measurements, and for the low temperature crystals.The data were interpreted in terms of two conformers, anti and gauche, in the vapour and liquid state and one, the anti, in the crystalline forms. A phase transition for 1,5-hexadiyne was observed at ca. 240 K. Both the high and low temperature crystals had molecules in the anti conformer.Interpretation of the spectra in terms of conformational equilibria was facilitated by a thorough vapour phase band contour analysis. With a few exceptions, all the vibrational fundamentals for both conformers were assigned and found to be in good agreement with results from normal coordinate calculations.     

The vibrational spectra of 1,1,4,4-tetrafluoro- and 1,1,4,4-tetrachlorobutadiene

Raman data are reported for gas, liquid and solid 1,1,4,4-tetrafluorobutadiene, F₂CCHCHCF₂, and IR data for gas and solid. The molecule has a planar trans conformation of C_2h symmetry. With the aid of Raman depolarization ratios and IR band contours, twenty of the twenty-four spectroscopically-active fundamentals can be assigned with assurance. Frequencies are suggested for the remaining four modes.Raman and IR data are reported for the liquid and solid 1,1,4,4-tetrachlorobutadiene. Mid-IR gas phase data are also reported. Again the data can be satisfactorily explained under C_2h symmetry. Fourteen fundamentals can be assigned with confidence. Suggestions have been made for the frequencies of nine other fundamentals.     

Vibrational spectra and thermodynamic functions of allyl acetate

Raman spectrum of allyl acetate molecule has been photographed in liquid phase using 4358 ? line of mercury arc as the exciting line. Infrared absorption spectrum of the molecule has been recorded in liquid phase in the frequency range 200–4000 cm⁻¹. Both the spectra have been analysed to identify the fundamental frequencies. AssumingC _s symmetry, the observed fundamental frequencies have been assigned to various modes of vibration and compared with the frequencies of allyl halides and acetic acid. On the basis of present assignments of fundamental vibrational frequencies and assumed approximate structural parameters of the molecule, thermodynamic functions have been computed.     

Simulation of the Raman spectra of zwitterionic glycine + nH2O (n = 1, 2, …, 5) by means of DFT calculations and comparison to the experimentally observed Raman spectra of glycine in aqueous medium

Raman spectra of an aqueous solution of glycine (Gly) have been recorded in the range of 400-2000 cm⁻¹. In aqueous solution, glycine molecules exist in their zwitterionic form, having two opposite charged poles, COO⁻ and NH₃⁺. The zwitterionic structure of glycine (ZGly) is stabilized by the hydrogen bond interaction of water (W) molecules. In the present report, we have optimized the ground state geometries of different hydrogen bonded complexes of [ZGly + (W)_n=1-5] in aqueous medium using DFT calculations at the B3LYP/6-311++G(d) level of theory. A comparative discussion on the structural details and binding energies (BEs) of each conformer has been also done. The theoretical Raman spectra were calculated corresponding to the most stable [ZGly + (W)_n=1-5] conformers. The theoretically simulated Raman spectra of each stable conformer were compared with experimentally observed Raman spectra to explore the number of water molecules needed for stabilizing the structure of ZGly. The theoretically simulated Raman spectra corresponding to the most stable conformer of [ZGly + (W)₅] having a BE of −22.8 kcal/mol, are matching nicely with the experimentally observed Raman spectra. Thus, on the basis of the above observations, we conclude that the conformer, [ZGly + (W)₅] is the most probable conformer in the aqueous medium. We also believe that in the conformer, [ZGly + (W)₅] the five water molecules are arranged around the ZGly in such a way that the effect of steric hindrance is less compared to the other conformers. The dipole-dipole interaction potential (DDP) is also calculated corresponding to the strongest hydrogen bond for each [ZGly + (W)_n=1-5] conformer.     

On the conformational characteristics of the O,O,O-trimethyl selenophosphate molecule

Spectroscopic and theoretical studies were carried out for O,O,O-trimethyl selenophosphate molecule. DFT structural and vibrational calculations were performed at 6-311++G^∗∗ level. Ar/matrix-FTIR spectra were recorded. A coexistence of different conformers with C₃ and C₁ symmetries was detected at different temperatures. Spectral evidence of a lower energy C_s conformer was found. These conclusions are consistent with the results from DFT calculations. A tentative assignment of the features observed in the Ar/matrix-FTIR spectra is proposed.     

Vibrational spectra and structure of cyclopropane-d1 and dicyclopropyl ketone

Infrared spectra have been obtained for cyclopropane-d₁, C₃H₅D(CP-d₁), in the vapor phase and for dicyclopropyl ketone (C₃H₅)₂ CO (DCPK) in the liquid state. Raman spectra of the latter compound in the liquid and solid phases have also been recorded. By comparing the experimental with the theoretical spectra of CP-d₁ it has been possible to assign most of the fundamental frequencies of the molecule. Additionably, empirical spectra—structure correlations from the literature for cyclopropyl derivatives containing the COX moiety (X=halogen) have been used to investigate the conformational preference of DCPK. The experimental results confirm that the molecular configuration with the carbonyl group cis to the planes of the two rings is the predominant species in the liquid state, though evidence for a second conformer, which we tentatively identify as the cis—trans conformer, is presented.