The vibrational spectra and normal coordinate analysis of tetracyclopropyllead

All the fundamental frequencies observed in IR and Raman spectra have been assigned to the normal modes of the molecule (C₃H₅)₄Pb (C₃H₅ = cyclopropyl). The calculated force field is compared to that of (C₃H₅)₂Hg and the Cmetal stretching force constants are discussed along with those of Me₄Pb and Me₂Hg; The similarity of the spectra of cyclopropyllead and cyclopropyl-mercury proves that the vibrations of cyclopropyl structural units are isolated in both molecules.     

Far infrared spectra,vibrational assignment and normal coordinate analysis of the tricyanomethanideion

Far infrared spectra of the tricyanomethanide ion C(CN)₃^? in solution and in the solid state have been investigated. The results allow a complete vibrational assignment to be made. A normal coordinate analysis has been carried out, the results of which are compatible with the existence of some double bond character in the C-C bonds of C(CN)₃^?.     

Infrared spectra,vibrational assignment,normal coordinate analysis and thermodynamic functions of tetracyanomethane

The infrared spectrum of tetracyanomethane in acetonitrile solution has been recorded and the full set of fundamental frequencies assigned. A normal coordinate analysis has been carried out and the values of the calculated force constants are compared with those of related molecules. Some thermodynamic functions have also been computed.     

Structure,vibrational assignment,normal coordinate analysis,and ab initio calculations of methylisocyanate

The infrared (3200-30 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra of gaseous and solid methylisocyanate, CH3NCO, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios have been measured. The CNC bend has been observed in the far infrared and low frequency Raman spectra of the gas at approximately 172 cm⁻¹. An additional far infrared band at ≈50 cm⁻¹ has tentatively been assigned as the methyl torsional mode, although it could be due to the Δν = 1, Δl = ± 1 transitions of the CNC bending mode. A complete assignment of the vibrational fundamentals is proposed. The structural parameters, force constants, and vibrational frequencies have been determined from ab initio Hartree—Fock gradient calculations using the 6-31G* basis set. Additionally, structural parameters have been obtained with the 6-311 + + G** basis set with electron correlation at the MP2 level which are compared to those obtained from the microwave data and electron diffraction study. These results are compared with the corresponding quantities obtained for similar molecules.     

Conformational and vibrational analysis with the aid of normal coordinate calculations

Many organic compounds exist as equilibrium mixtures of two or more molecular conformations, and vibrational spectroscopy can be used to obtain information about the structure of those conformations. Normal coordinate calculations are often an aid to those conformational studies and to making vibrational assignments for the different conformers. However, sometimes those calculations are partially inconclusive, and a few results are briefly discussed in which both conclusive and inconclusive results were obtained from calculations. Calculations are then applied to some 1,2-dichloro- and 1,2-dibromo-alkanes. Previous calculations on 1,2-dichloropropane and 1,2-dichlorobutane are revised, and calculations are reported for 1,2-dibromopropane, 1,2-dibromopropane-d₆, and 1,2-dibromobutane. Spectra are given for the last two of these compounds. A modified valence force field was determined for each family of 1,2-dihaloalkane that should be transferable to other members of the family.     

Vibrational spectrum and normal coordinate analysis of SF5Br

The i.r. spectrum of gaseous and the Raman spectrum of liquid SF₅Br are reported. Ten out of 11 fundamentals expected for symmetry C_4υ were observed and assigned. A normal coordinate analysis was carried out and thermodynamic properties in the range 0–2000 K were computed.     

Far-infrared spectrum,conformational stability,barriers to internal rotation,normal coordinate calculations,and vibrational assignment for chloroacetaldehyde

The far infrared spectrum [350 to 25 cm^–1] of gaseous chloroacetaldehyde, ClCH₂CHO, has been recorded at a resolution of 0.10 cm^–1. The first excited-state transition of the asymmetric torsion of the more stable near s-cis [chlorine atom s-cis to the aldehyde hydrogen atom] conformer has been observed at 26.9 cm^–1, with seven additional upper state transitions falling to higher frequency. Additionally, the fundamental torsional transition of the s-trans conformer has been observed at 58.9 cm^–1 with two excited states also falling to higher frequency. From these data, the asymmetric torsional potential coefficients have been determined to be:V ₁=414±11;V ₂ = 191±3;V ₃=–203±5;V ₄=44±1 andV ₆=–26±1 cm^–1. The s-cis to s-trans barrier is 500±5 cm^–1 (1.43±0.01 kcal mol^–1) with the s-cis conformer being more stable by 267±19 cm^–1 (0.76±0.05 kcal mol^–1) than the s-trans form. The Raman [4000 to 100 cm^–1] and infrared (4000 to 400 cm^–1] spectra of the gas have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Complete vibrational assignments are proposed for both conformers based on band contours, depolarization values, and group frequencies. The assignments are supported by ab initio Hartree-Fock gradient calculations employing the 3–21G^* basis set to obtain the frequencies and the potential energy distributions for the normal vibrations for both rotamers. Additional ab initio calculations at the MP4/6-31G^* level have been carried out to determine the structural parameters for both conformers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.This contribution taken in part from the thesis of C. L. Tolley which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

The vibrational spectra and normal coordinate analyses of cubic and monoclinic SiP2O7

The infrared and Raman spectra of cubic and monoclinic SiP₂O₇ were measured and interpreted by normal coordinate analyses using a modified valence force field. Band assignments were made for the vibrational modes of these materials, including those that involved the SiO₆ units. The calculated force constants for the SiO₆ and the P₂O₇ units were consistent with those for SiO₄- and P₂O₇-containing materials as well as stishovite. The Si-O stretching force constants for the SiO₆ units were considerably lower than those for SiO₄ units.     

Conformational stability,barriers to internal rotation,normal coordinate analysis,and vibrational assignment of chloroacetyl bromide

The infrared spectra (3200 to 30 cm^–1) of gaseous and solid chloroacetyl bromide, CH₂ClC(O)Br, and the Raman spectra (3200 to 10 cm^–1) of the gas, liquid (with depolarization data), and solid have been recorded. From the observed asymmetric torsional transitions, the potential function governing internal rotation of the CH₂Cl moiety has been determined with the following coefficients:V ₁=336±11,V ₂=73±10,V ₃=757+7,V ₄=103±3, andV ₆=5±2 cm^–1. This potential function is consistent with s-trans to gauche and gauche to gauche barriers of 963±11 and 709±12cm^–1, respectively, and enthalpy difference of 373 ± 24 cm^–1 with the dihedral angle of the gauche rotamer being 115°. The enthalpy difference has been determined experimentally from the studies of the Raman spectra at different temperatures to be 359±68 cm^–1 (1.03±0.19 kcal mol^–1) and 507±24 cm^–1 (1.45±0.07 kcal mol^–1) for the gas and liquid, respectively, with the s-trans conformer being the more stable conformer in the gas and liquid and the only one present in the annealed solid. A complete assignment of the vibrational fundamentals is proposed from spectral data obtained for the gas, liquid, and solid. The assignment is supported by a normal coordinate calculation utilizing a modified valence force field to obtain the frequencies for the normal vibrations and the potential energy distribution. The results are discussed and compared to the corresponding quantities for some similar molecules.Taken in part from the thesis of H. V. Phan, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

The infrared matrix isolation spectrum and normal coordinate analysis of the Beryllium Fluoride Dimer

The infrared spectra of the beryllium fluoride vapor species isolated in matrices of neon and argon were obtained in the range (2000–190) cm^?1. Four frequencies were identified as belonging to the dimer Be₂F₄. Assuming the latter to have a planarbridge structure of D_2h symmetry, the frequencies in a neon matrix were tentatively assigned. A normal coordinate analysis of the dimer molecule is presented together with the calculated vibrational frequencies and the calculated mean amplitudes of vibration.     

The vibrational spectra,rotational isomerism,normal coordinate analysis and mean amplitudes of ethyl formate,ethyl chloroformate and ethyl cyanoform

The infrared spectra of ethyl formate, chloroformate, and cyanoformate in the liquid phase have been recorded in the region 4000–4020 cm^?1, and in the solid and vapour phase and in solution in the region 4000–4200 cm^?1. Evidence is reported for the existence of two rotameric forms in each case.Normal coordinate calculations are reported for both rotameric forms of the first two esters, and assignments based on potential energy distributions are given. These assignments show considerable mixing of the normal modes and suggest the inadequacy of simple assignments made by comparison with related molecules.Calculated mean amplitudes are also reported for the first two molecules.     

Matrix i.r. spectrum and normal coordinate analysis of trifluoromethanethiol

The i.r. spectra of trifluoromethanethiol (CF₃SH) in solid argon and nitrogen have been recorded. A vibrational assignment based on normal coordinate analysis is presented. Potential energy distributions and the modified Urey-Bradley potential parameters are reported.     

The vibrational spectrum of the normal and perdeuterated tetramethylammonium ion

Rather complete Raman and i.r. spectra of the two isotopic ions in aqueous solutions have been obtained and qualitatively interpreted.Some revisions of previous assignments are suggested, based on the new data and the isotopic frequency shifts. The presence of complex Fermi resonances was found in the CD stretching range.     

Vibrational spectra and normal coordinate analysis of CF3 compounds: Part XLVI. Synthesis,vibrational spectra,normal coordinate analysis and electron diffraction investigation of the cis isomer of hexafluoroazomethane

The hitherto unknown cis isomer of hexafluoroazomethane has been prepared by the reaction of CICN with AgF₂ under mild conditions. It isomerizes rapidly to the trans isomer when exposed to daylight, but is stable in the dark. The compound has been characterized by NMR and UV spectra. Infrared and Raman spectra have been recorded and assigned with the assistance of a normal coordinate analysis. The molecular structure of cis-CF₃NNCF₃ has been determined by gas phase electron diffraction, and a planar CNNC skeleton, d(NN) 1.229(8) Å, d(CN) 1.494(5) Å, and ∠NNC 122.1(8)° has been established. Compared with the trans isomer, the higher sterc strain due to F?F repulsions is released by a ∮.03 Å d(CN) lengthening and a 9° widening of the NNC angle.     

Infrared spectra and normal coordinate analysis of 2-chloroethanol

The i.r. spectra of 2-chloroethanol and its OD-deuterated analogue have been recorded in argon and nitrogen matrices and in the gas phase. Raman spectra in the liquid state have been recorded. A vibrational assignment, supported by normal coordinate calculations, is presented. A conformational change from gauche to trans conformer was noted under the i.r. beam.     

Some periodic trends,molecular structure,normal coordinate analysis of 1,3,5-trioxane, -trithiane and -triselenane: computational and vibrational studies

The Raman (3200–100 cm⁻¹) and infrared spectra (3200–200 cm⁻¹) of solid C₃H₆O₃ (TO) and C₃H₆S₃ (TS) have been recorded and only the chair conformation is present. Furthermore, utilizing the CH stretching bands at the infrared spectrum of the gaseous phase, the CH_ax and CH_eq distances are found to be 1.088 and 1.107 Å, respectively. The structural parameters and conformational stabilities for 1,3,5-C₃H₆X₃ series (where X=O, S and Se atoms) have been obtained from density functional theory at the Becke3-LYP gradient-corrected functional (DFT-B3LYP) and from MP2 level with full electron correlation. These calculations have been extended up to 6-311++G(d,p) basis set to include polarization and diffusion functions. All computational results and vibrational analysis are in favor of the chair conformation (C_3v), whereas the boat (C₁) and Planar (D_3h) forms have been excluded owing to the predicted imaginary wavenumber(s). According to 6-311++G(d,p) basis set, the ring size and the tendency of the ring to undergo flattening is found to be directly proportional to the atomic size of the substituted hetero atoms (X) of the chair. The calculated DFT-B3LYP scaled quantum chemistry (QC) force fields at 6-31G(d) basis set lead to a number of revised assignments for certain vibrational modes and it appears to give quite accurate Raman spectra for the investigated chalcogenanes. The estimated bond lengths, bond angles, rotational constants, Raman activities dipole moment and unscaled force constants are compared with either theoretical and/or experimental results whenever possible.     

Infrared, and Raman spectra, conformational stability, normal coordinate analysis, ab initio calculations, and vibrational assignment of 1-chlorosilacyclobutane

The infrared spectra (3500–40 cm⁻¹) of gaseous and solid and the Raman spectra (3500–30 cm⁻¹) of liquid and solid 1-chlorosilacyclobutane, c-C₃H₆SiClH, have been obtained. Both the axial and equatorial conformers with respect to the chlorine atom have been identified in the fluid phases. Variable temperature (−105 to −150°C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference has been determined to be 211±17 cm⁻¹ (2.53±0.21 kJ/mol), with the equatorial conformer being the more stable form and the only conformer remaining in the annealed solid. At ambient temperatures, approximately 26% of the axial conformers are present in the vapor phase. A complete vibrational assignment is proposed for the equatorial conformer, and many of the fundamentals of the axial conformers have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been determined for both rotamers by ab initio calculations employing the 6-31G(d) basis set at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. Structural parameters have also been obtained using MP2/6-311+G(d,p) ab initio calculations. The r₀ parameters for both conformers are obtained from a combination of the ab initio predicted values and the twelve previously reported microwave rotational constants. The results are discussed and compared to those obtained for some similar molecules.     

Ab initio study of vibrational frequencies,force field and normal coordinate analysis of the cis- and trans-isomets of nitrosomethanol

In this paper, the equilibrium geometries of two isomers of the newly found compound — nitrosomethanol—have been optimized by ab initio SCF MO method with 3–21G basic set by gradient technique. And the second derivatives of potential energy (i. e. the force constant matrix elements) have been calculated analytically. Hence the entire force fields of the two isomers of nitrosomethanol have been obtained theoretically. The theoretical vibrational frequencies and the corresponding normal modes were obtained and compared with the experimental values, and the structures of two isomeric forms of nitrosomethanol are established.     

Vibrational spectra,assignments and normal coordinate analysis of 2-amino-5-bromopyridine

The FTIR and laser Raman spectra of 2-amino-5-bromopyridine 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.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.