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.     

Spectra and structure of phosphorus—boron compounds—XXVI. Infrared and Raman spectra,conformational stability and normal coordinate analysis of ethyldichlorophosphine-borane

The Raman (3500-10 cm⁻¹) and infrared (3500-50 cm⁻¹) spectra of solid ethyldichlorophosphine-borane, CH₃CH₂P(BH₃)Cl₂ and its deuterated analog, CH₃CH₂P(BD₃)Cl₂ have been recorded. Additionally, the infrared spectra of the gases and the Raman spectra of the liquids have been recorded and qualitative depolarization ratios have been obtained. Based on the fact that several distinct Raman lines disappear on going from the liquid to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers, with the trans conformer being more stable in the liquid phase, and the only one present in the solid phase. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be nearly zero. Based on Raman depolarization data, group frequencies, isotopic shift factors and infrared band contours, a complete vibrational assignment has been proposed for the trans conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The BH₃ torsion has been observed at 188 cm⁻¹, while the BD₃ torsion was not observed. The methyl torsions in the spectra of the solids have been observed at 209 and 202 cm⁻¹ for the “light” and deuterated species, respectively. From the torsional data, barriers to internal rotation have been calculated. The asymmetric torsional mode has been observed for the trans conformer in the infrared spectra of the gas phase at 108 and 104 cm⁻¹ for the BH₃ and BD₃ species, respectively. These results are compared with similar quantities for some corresponding organophosphine—borane compounds.     

Simulation of vibrational spectra of isotopic benzenes by an extended molecular mechanics method

Vibrational spectra of benzene and benzene-d₆ in the gas and liquid phase have been simulated by a molecular mechanics method including the calculation of equilibrium structures, thermodynamic quantities, normal frequencies and vibrational transition probabilities. The potential parameters have been estimated by referring to the observed frequencies of benzene, benzene-d₆ and 1,3,5-benzene-d₃ and also to results of ab initio calculations. Four and ten independent parameters are required, respectively, for elucidating the infrared absorption and Raman intensities of these compounds in the gas and liquid phase. The infrared absorption spectrum of benzene-d₁ is reproduced well by using the potential and the intensity parameters estimated for benzene and benzene-d₆. The change of relative band intensities on the phase change has been elucidated in terms of the change of various intensity parameters.     

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.     

The vibrational spectra of maleimide and N-D maleimide

The infrared spectra of maleimide as a vapour (160°C), melt (100°C), oriented polycrystalline film, pellet and when dissolved in various solvents were recorded between 4000 and 400 cm^?1. Also certain spectra in the far infrared region 400-40 cm^?1 were obtained. Raman spectra of the crystalline solid, melt and as a saturated solution in acetonitrile were recorded and semiquantitative polarization measurements carried out. For N-D maleimide infrared and Raman spectra of the solid compound were recorded.The fundamental frequencies have been assigned in terms of C_2v, symmetry on the basis of infrared vapour contours and dichroism of the oriented film as well as on Raman polarization data. A force field was derived for maleimide, by initially transferring force constants from maleic anhydride and subsequent refinement of the force constants. The agreement between observed and calculated frequencies for the in-plane modes was satisfactory whereas certain large discrepancies remained for the out-of-plane vibrations.     

Vibrational spectra of the trans-trans and trans-cis conformers of dimethyl fumarate

Infrared and Raman spectra of dimethyl fumarate (DMFU) have been recorded in the temperature range 12–390 K. The solid state spectra are consistent with the trans-trans conformation. However, in the liquid phase (melt or solution in CCl₄) and in the vapour phase, additional infrared and Raman bands were observed due to the presence of the trans-cis conformer. For the trans-trans conformer the observed spectra have been assigned on the basis of a C_2h molecular symmetry. A normal coordinate analysis of trans-trans DMFU has been carried out using a modified Urey- Bradley force field to assist in the assignment. Observed frequencies for the trans-cis conformer have been assigned on the basis of a structure of C_s symmetry.     

Theoretical anharmonic Raman and infrared spectra with vibrational assignments for monofluoroaniline isomers

The ortho-meta-, and para-fluoro substituted anilines are prototype molecules for investigation of the interactions of both the amino group and the fluorine atom with the aromatic ring. The molecular structures, natural atomic charges and theoretical anharmonic Raman and infrared spectra of the three fluoroaniline isomers have been calculated by using the density functional B3LYP method with the extended 6-311++G(df,pd) basis set. The Raman and infrared spectra of 2FA, 3FA, and 4FA have been recorded. The detailed vibrational assignments of the experimental spectra have been made on the basis of the calculated potential energy distributions, PEDs. The effect of fluorine substituent on the aniline ring geometry and charge distribution, the nature of the characteristic “marker bands” and a quenching of intensities of some bands are discussed. It is shown that the frequencies of the NH₂ stretching vibrations depend on the degree of pyramidalization of the C-NH₂ group, in the isomers. In 2FA and 3FA, the NH₂ stretching frequencies are higher than those in 4FA. This corresponds to a more flattened structure of the amino group in 2FA and 3FA, in comparison to 4FA.     

Bildung siliciumorganischer verbindungen: 52. Das schwingungsspektrum von 1,3,5,7-tetramethyl-tetrasilaadamantan

The infrared and Raman spectra of 1,3,5,7-tetramethyltetrasilaadamantan, Si₄C₁₀H₂₄, have been recorded over the ranges 4000–4200 and 1500–1550 cm^?1 respectively. The fundamentals can be assigned completely on the basis of T_d-symmetry. An approximate normal coordinate analysis has been performed, including three A₁, four E and nine F₂ frequencies. The resulting force constants are in complete agreement with the literature data reported for SiC compounds.     

Calculation of the frequencies and intensities in the infrared and raman spectra of cyclopropenone

By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II-d₀ , II-d₂ ) and ¹⁶ O-and ¹⁸ O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants.     

Infrared,Raman and NMR spectra,conformational stability,and ab initio calculations of divinylmethoxyborane

The infrared spectra (4000–50 cm⁻¹) of gaseous and solid divinylmethoxyborane, (CH₂=CH)₂BOCH₃, as well as the Raman spectra (3500–20 cm⁻¹) of the liquid and solid have been recorded. Qualitative depolarization values have been obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, have been assigned based on infrared band contours, depolarization values, group frequencies, and normal coordinate calculations. From a comparison of the spectra in the fluid and solid states, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes have been calculated with the 3–21G basis set. A comparison of these calculated frequencies to the observed spectra is consistent with the predominant form having a “planar” heavy atom skeleton with C_s, symmetry. From the variable low temperature ¹³C NMR data, a barrier to rotation about the B-O bond of 10.1 ± 0.1 kcal mol⁻¹ has been determined, which is in excellent agreement with a barrier of 8.5 kcal mol"1 obtained from ab initio calculations. Structural parameters, conformational stability, and barriers to internal rotation have been obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21G and 6–31G^* basis sets. The results are compared to the corresponding data for some similar organoboranes.     

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.     

Raman and infrared spectra of GdTb (MoO4)3 single crystal in the region 250–1000 cm−1

Polarized Raman spectra (single crystal) at 300 K and infrared spectra (powder) at 300 and 85 K in the region 250–1000 cm⁻¹ of a binary molybdate of gadolinium and terbium have been recorded. Based on C_2ν symmetry, group theoretical analysis has been carried out and vibrational assignment is proposed. The observed symmetric stretching frequencies of the MoO²⁻₄ ion points to the absence of resonance vibrational interaction in this system.     

Investigation of Raman and infrared phonon modes in case of barium bismuth tantalate (BaBi2Ta2O9)

The Raman and the infrared wavenumbers in the Aurivillius structure BaBi₂Ta₂O₉ (BBT) having space group I4/mmm (no. 139-D_4h¹⁷) are investigated using normal coordinate analysis. The calculation of zone center phonons incorporates seven stretching and seven bending force constants. The Raman and the infrared frequencies for BBT have been assigned for the first time in I4/mmm phase. The calculated Raman and infrared wavenumbers are in very good agreement with the observed ones. The potential energy distributions (PED) are also investigated for each normal mode in BBT and the contributions of different force constants to various frequencies are determined.     

Raman and i.r. spectra of tetramethylcyclobutanedione and the fully deuterated derivative

Raman spectra of tetramethylcyclobutane-1,3-dione (TMCBD) as a polycrystalline solid and in solution in benzene and carbon tetrachloride have been recorded. Infrared and Raman spectra of the fully deuterated molecule have also been recorded. The spectra are consistent with predictions based on a centrosymmetric molecule with a planar cyclobutadione ring and point group D_2h. A fairly complete assignment of the observed spectra is presented for both molecules. A correlation of the frequencies of the fundamentals of TMCBD-h₁₂ and - d₁₂ has been made. Ground state frequencies of fundamentals involved in progressions in the n-π* electronic spectrum have been located.     

Spectra and structure of organophosphorus compounds—XXXVII. Infrared and Raman spectra,conformational stability,vibrational assignment and normal coordinate analysis of ethyldichlorophosphine-d0 and -d5

The infrared (3500 to 40 cm⁻¹) and Raman (3500 to 10 cm⁻¹) spectra have been recorded for the gaseous and solid phases of ethyldichlorophosphine, CH₃CH₂PCl₂, and CD₃CD₂PCl₂. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. In the spectrum of the gas the gauche conformer is predominant with about 65% abundance whereas in the spectrum of the liquid at ambient temperature the amount of gauche conformer is reduced compared to the gas phase and at −100°C the trans conformer predominates. The trans conformer is the more stable species in the solid. A variable temperature study was carried out on the Raman spectrum of the liquid and ΔH and ΔS values of 190 ± 30 cm⁻¹ (543 ± 87 cal/mol) and 2.86 ± 0.3 eu were determined, respectively, with the trans conformer being more stable. Similar variable temperature studies have been carried out on a number of conformer peaks in the infrared spectrum of the gas and a ΔH value of 53 ± 38 cm⁻¹ (152 ± 110 cal/mol) was obtained, again with the trans conformer being more stable. All the fundamental modes of both conformers have been assigned utilizing band contours, depolarization values, isotopic shift factors and group frequencies. A normal coordinate calculation has been carried out utilizing a modified valence force field to calculate the frequencies and potential energy distribution for both conformers. The barriers to methyl rotation of the trans and gauche conformers are 2.2 ± 0.1 and 2.3 ± 0.1 kcal/mol, respectively. These results are compared to similar quantities for some corresponding molecules.     

Accurate theoretical IR and Raman spectrum of Al2O2 and Al2O3 molecules

The accurate harmonic vibration frequencies together with the infrared (IR) and Raman intensities of the most stable conformers of Al₂O₂ and Al₂O₃ molecules have been calculated by the density functional theory (DFT) method with B3LYP exchange–correlation potential and using a set of the augmented correlated consistent basis sets up to quintuple order. The anharmonic vibration frequencies of the non-linear Al₂O₂ molecule have also been calculated. The obtained equilibrium geometrical parameters, harmonic and anharmonic vibration frequencies along with the IR and Raman intensities good converge to their limits with increasing the size of the used basis set. A comparison of the calculated harmonic and anharmonic vibrational frequencies with the available experimental ones points out that the small differences between the calculated harmonic and experimental frequencies can be further substantially reduced when calculations of the anharmonic vibrational frequencies will be available for all types of molecular geometries.     

Vibronic spectra and normal coordinate analysis of substituted anilines—I. 2,3-, 2,4-, and 2,5-dimethylanilines

Vibronic spectra of 2,3-, 2,4-, and 2,5-dimethylanilines (DMA) have been recorded in the vapor phase and analysed primarily for ascertaining the frequencies of certain low lying fundamentals (< 1000 cm⁻¹) which were observed earlier in infrared and Raman spectra with rather poor intensities. In most cases, the investigation of vibronic spectra has supported the data observed in infrared and Raman spectra. However, a new frequency has been observed at ∼120 cm⁻¹ in each molecule and has been assigned to the CNH₂ out-of-plane wag. A detailed analysis of the vibronic spectra of these three molecules revealed that an interaction-induced blue-shift of nearly 1700 cm⁻¹ is caused in the (0, 0) band of all the three DMAs due to an electrostatic interaction between the NH₂ and CH₃ groups.The normal coordinate analyses (NCA) of the above three molecules have been carried out using a general valence force field (GVFF) with 21 principal and 30 interaction force constants, assuming an averaged structure, a planar geometry, and a C_s symmetry in each case. The fundamental frequencies were mostly taken from an earlier work reported from this laboratory. Some frequencies were also picked up from the investigation of the vibronic spectra reported herein. The force field calculations were carried out using the least-squares iterative technique. During final calculations, all the 51 force constants were allowed to iterate simultaneously, which reproduced the 52 experimentally observed fundamentals out of the 54 (35a′+ 19a″) expected ones within an average error of ± 1.0% with a reasonable potential energy distribution (PED) among the various normal modes.     

Electron spin relaxation in liquids : edited by L.T. Muus and P.W. Atkins,Plenum Press,New York, 1972, pp. xiv + 537, price £29.50

The infrared and Raman spectra of trimethylarsine sulfide, trimethylarsine selenide, and their perdeuterated analogues have been recorded. An assignment of 22 of the 24 fundamental vibrational frequencies (exclusive of the methyl torsions) has been made for each molecule. Assignments were made on the basis of symmetry selection rules and comparison with structurally similar molecules.A normal coordinate analysis for each of these molecules was carried out to reinforce the assignments. Assuming a valence force field for each molecule of C_3v symmetry, a set of 24 force constants was refined to give a least squares fit of the calculated frequencies to the observed frequencies. Calculations of the potential energy distribution for each molecule show that there exists little coupling between the different modes.     

Spectra and structure of organogermanes: Part XX. Infrared and Raman spectra of (CH3)3GeNCO and (CH3)3GeNCS

The infrared and Raman spectra of gaseous and solid (CH₃)₃ GeNCO and solid (CH₃)₃GeNCS have been recorded over the frequency range 20–4000 cm^?1 . The Raman spectra of the liquids have also been recorded. Assignments of the normal modes have been made on the bases of band types, Raman depolarization values, and characteristic frequencies. Spectral data indicate that (CH₃)₃ GeNCO is non-linear in all phases and that (CH₃)₃GeNCS has a linear or quasi-linear heavy atom skeleton in the fluid phases.     

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.