Raman spectra of gases: XIV. Hexachlorodisiloxane

The Raman spectra (50–1200 cm^?1) of gaseous, liquid, and solid (Cl₃Si)₂O have been recorded. The infrared spectra of the gas and solid have been recorded from 55–2000 cm^?1 . The spectra of the gas have been interpreted in detail on the basis of C_2v symmetry with the A₁ skeletal Si-O-Si bend assigned at 63 cm^?1. The spectra gave evidence that there are structural changes upon condensation of the gas and the Si-O-Si angle approaches linearity in the solid state. The opening of this angle is probably due to crystal packing factors.     

Infrared and Raman spectra and normal coordinate calculations for methylisothiocyanate

The infrared spectra (3200-50 cm^?1) of gaseous and solid CH₃NCS and CD₃NCS and the Raman spectra (3200-10 cm^?1) of the liquids and solids have been recorded. The spectra have been interpreted on the basis of a “pseudo-symmetric top” with C_3v symmetry. An assignment of the fundamental vibrations in both molecules, based on their infrared band contours, depolarization values and group frequencies, is given and discussed. Particularly interesting is the low-frequency region where band maxima were observed at 152 and 80 cm^?1 for CH₃NCS and 139 and 71 cm^?1 for CD₃NCS in the infrared spectra of the gases. A normal coordinate analysis has also been carried out based on C_3v symmetry. Considerable mixing was found between the C_αN stretch and NCS symmetric stretch in both isotopic species. The other normal modes in CH₃NCS are reasonably pure but, for the CD₃NCS molecule, considerable mixing was found between the CD₃ stretches and NCS antisymmetric stretch. The proposed vibrational assignment and the results of the normal coordinate calculations are discussed and compared with the results obtained for similar molecules.     

Spectra and structure of organophosphorus compounds: XVII. Infrared and Raman spectra. vibrational assignment and barriers to internal rotation for t-butylphosphine

The infrared spectra of gaseous and solid tertiary-butylphosphine, [(CH₃)₃CPH₂], have been recorded from 50 cm^?1 to 3500 cm^?1. The Raman spectra of gaseous, liquid and solid (CH₃)₃CPH₂ have been recorded from 10 to 3500 cm^?1. A vibrational assignment of the 42 normal modes has been made. A harmonic approximation of the methyl torsional barrier from observed transitions in the solid state gave a result of 4.22 kcal mol^?1 and 3.81 kcal mol^?1 in the gaseous state. Hot band transitions for the phosphino torsional mode have been observed. The potential function for internal rotation about the C-P bond has been calculated. The two potential constants were determined to be: V₃ = 2.79 ± 0.01 kcal mol^?1 and V₆ = 0.07 ± 0.01 kcal mol^?1.     

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.     

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.     

Infrared and Raman spectra,vibrational assignment and normal coordinate calculations for ethylisothiocyanate-d0 and -d5

The i.r. spectra (3500-40 cm⁻¹) of gaseous and solid ethylisothiocyanate, CH₃CH₂NCS, and ethylisothiocyanate-d₅, CD₃CD₂NCS, and the Raman spectra (3200-10 cm⁻¹) of the liquids and solids have been recorded. Additionally, the i.r. spectrum of matrix (N₂) isolated CH₃CH₂NCS was recorded from 3500 to 200 cm⁻¹. The vibrational spectra have been interpreted on the basis of a cis form of C_s symmetry for all three physical states; however, in the spectum of the matrix isolated sample at 10 K, several of the fundamentals are doublets which may be arising from two conformers at this temperature. A vibrational assignment is given based on i.r. band contours, depolarization values, isotopic shifts and group frequencies. The assignment is supported by the Teller—Redlich product ratios. The methyl torsion was observed at 270 cm⁻¹ in the solid phase which gives a periodic barrier of 4.7 kcal/mole. A normal coordinate calculation has been carried out utilizing a modified valence force field consisting of 15 diagonal force constants and seven interaction terms which reproduced the observed frequencies with an error of 1.45% for the -d₀ molecule and 3.40% for the -d₅ compound. Because of the large CNC angle (∼ 145°) and low barrier to internal rotation of the asymmetric rotor, the skeletal bend and torsion couple to give a very broad band with two maxima and apparent P band heads. These results are compared to corresponding studies of similar molecules.     

Spectra and structure of gallium compounds: Part III. vibrational studies of trimethylgallane-phosphine and trimethylgallane-phosphine-d3

The IR (80–4000 cm^?1) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaPH₃ and (CH₃)₃GaPD₃ have been recorded for the solid state at low temperature. The spectra are interpreted on the basis of C_3v molecular symmetry. A modified valence force field model is utilized in calculating the frequencies and the potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis base moiety, and the differences are shown to be consistent with structural changes upon adduct formation. Only very minor coupling is found between the Ga-C₃ stretches and the CH₃ deformations and the remaining normal modes are nearly pure. The relative values of the force constants are compared to the corresponding quantities in other Group IIIA-Group VA coordinated complexes.     

Raman,infrared and NMR spectra and structure of divinylmethylborane

The Rarnan spectra of gaseous, liquid and solid divinylmethylborane have been recorded from 20–3500 cm^?1 and the IR spectra of gaseous and solid divinylmethylborane recorded over the range 30–3500 cm^?1. A variable temperature study of the Raman spectrum of the liquid phase has been carried out. A complete vibrational assignment is presented. In the solid phase the molecule appears to have a planar heavy atom skeleton (C_s symmetry). From analysis of the spectra of the fluid phases, the presence of a second isomer, in which one or both of the vinyl groups are twisted slightly out of the BC₃ plane (C₁ symmetry), is proposed. Variable temperature ¹³C NMR studies have been carried out. A comparison of the ¹³C chemical shift of C_β of the vinyl group with the corresponding value in other vinylboranes indicates that relatively little delocalization of the π-electron density occurs in this molecule. Low temperature (?115°C) ¹³C NMR data are consistent with a low barrier to rotation about the boron-vinyl carbon bond.     

Infrared and raman spectra,vibrational assignment and barriers to internal rotation for methyldisilylamine

The Raman spectra of gaseous and liquid (SiH₃)₂NCH₃ and (SiH₃)₂NCD₃ have been recorded to within 10 cm^?1 of the exciting line. The IR spectra of (SiH₃)₂NCH₃ and (SiH₃)₂NCD₃ have been recorded from 80 cm^?1 to 3800 cm^?1 in the gaseous state, and from 80 cm^?1 to 450 cm^?1 in the solid state. A vibrational assignment has been made, and from the low-frequency vibrational data, an upper limit of 3.3 kcal mol^?1 was calculated for the barrier to internal rotation of the silyi groups, whereas a barrier of ~450 cal was calculated for internal rotation of the methyl group. It is concluded that there exists a significantly strong d_π—p_π interaction in methyldisilylamine.     

Vibrational spectra and molecular symmetry of tetrasilylhydrazine and tetrasilylhydrazine-d12

The Raman spectra of tetrasilylhydrazine and tetrasilylhydrazine-d₁₂ have been recorded for the gas, liquid and solid phases from 25 to 2500 cm^?1. The infrared spectra of N₂(SiH₃)₄ and N₂(SiD₃)₄ have been recorded for the gas and solid phases from 40 to 2500 cm^?1. The vibrational data have been interpreted on the basis of a twisted (D_2d) molecular configuration for both the fluid and solid states.     

Spectra and structure of organophosphorus compounds—XXVIII. Vibrational and conformational analysis of dimethylmethoxyphosphine and some isotopically substituted derivatives

The i.r. spectra (3600-50 cm⁻¹) of the gaseous and solid states, and the Raman spectra (3600-10 cm⁻¹) of the gaseous, liquid and solid states of (CH₃)₂POCH₃, (CH₃)₂POCD₃, (CD₃)₂POCH₃ and (CD₃)₂POCD₃ have been recorded. Thirty-five of the 36 normal modes have been assigned and the asymmetric torsion has been observed as a broad weak feature centered at 106 cm⁻¹ in the far i.r. spectrum of gaseous (CH₃)₂POCH₃. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the amorphous and annealed solids indicates the existence of a second conformer present in a small amount in the gas phase but becoming more abundant in the liquid phase and the only remaining rotamer in the annealed solid. Asymmetric top i.r. band contour simulation provides evidence that the dominating species in the gas phase is one in which the methoxy methyl group is oriented approximately 60° (gauche) away from the lone pair of electrons on the phosphorus atom. The rotamer which remains in the spectra of the annealed solid has been assigned to a structure in which the lone pair on the phosphorus atom is oriented trans to the methoxy methyl group. These results are compared to similar data obtained for methoxy phosphoryl compounds and discussed in terms of both canonical molecular orbital and VSEPR thoery.     

Synthesis,characterization and vibrational investigation of divinylborinic anhydride

The new molecule divinylborinic anhydride [(CH₂CH)₂B]₂O as been prepared by the limited hydrolysis of divinylchloroborane. Characterization of the compound has included the preparation of 1 : 1 adducts with trimethylphosphine, dimethylphosphine and trimethylamine. Born-11 and carbon-13 NMR spectra have been obtained and have been interpreted in terms of mesomeric interactions between the empty boron pπ orbital and unshared pairs of electrons on oxygen as well as the pi electron system of the vinyl moiety. The Raman spectra (3500–200 cm^-1) of liquid and solid [(C₂H₃)₂B]₂O and the infrared spectra (3500–200 cm^-1) of gaseous and solid [(C₂H₃)₂B]₂O ¹ have been investigated for both the ¹⁶O and ¹⁸O isotopic species. The vibrational data indicate that the molecule possesses C₁ symmetry and a linear BOB angle.     

Raman and Infrared Spectra, Ab Initio Calculations, Normal Coordinate Analysis, and Conformational Stability of 2-Methoxypropene

The Raman (3500–40 cm^–1) and infrared (3500–70 cm^–1) spectra of gaseous and solid 2-methoxypropene, CH₃O(CH₃)C=CH₂, and the isotopomers, CD₃O(CH₃)C=CH₂ and CH₃O(CD₃)C=CD₂ have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with C_s symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm^–1 in the gas and 1.0 cm^–1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V₃ = 1485 ± 9 cm^–1 and V₆ = –55 ± 4 cm^–1 for the d₀ compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm^–1 and the C—CH₃ barrier is 772 ± 5 cm^–1. Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate.     

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.     

Conformational analysis,barriers to internal rotation and vibrational assignment for dimethylethylamine

The IR (50–3500 cm^?1) and Raman (20–3500 cm^?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol^?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH₃ rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol^?1, whereas the barrier for the CH₃ rotor of the ethyl group has been calculated to be 3.71 kcal mol^?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm^?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines.     

Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

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.     

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.     

Vibrational spectra and rotational barriers of methyl titanium halides CH3TiX3 and CD3TiX3 (X = Cl,Br, I)

The IR and Raman spectra of gaseous and solid CH₃TiX₃ and CD₃TiX₃ species (X = Cl, Br, I) are reported. The gas phase spectra have been recorded between 4000 and 20 cm^?1 at pressures of 1 atm and 4 atm at 350 K and the Raman spectra of the solid phase recorded at 4.2 K. Internal rotation barriers and thermodynamic functions have been calculated.