Vibrational spectra,assignments and normal coordinate analysis for difluorophosphine

Infrared spectra of the gas and Raman spectra of the liquid and solid forms of PF₂H and PF₂D are reported. A normal coordinate analysis based on compliance constants has been carried out on the assigned fundamentals and also on harmonic frequencies estimated by Dennison's method.     

Vibrational spectra,assignments and normal coordinate analysis of 3-aminobenzyl alcohol

The laser Raman and FTIR spectra of 3-aminobenzyl alcohol have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate analysis, 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.     

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.     

Vibrational spectra,assignments and normal coordinate analyses for crystalline zirconium tetrachloride and tetrabromide

Raman and far-IR spectra have been obtained of crystalline ZrCl₄ and ZrBr₄. The observed frequencies have been interpreted on the basis of the C_2h symmetry of the Bravais unit cell and have been subjected to a normal coordinate analysis. The interpretation and results are satisfactorily in accord with the X-ray structure.     

Vibrational spectra and normal coordinate analysis of carbamoylazide

The Fourier transform Raman and infrared spectra of carbamoylazide and its deuterated derivative were recorded and the observed frequencies were assigned to various modes of vibration in terms of fundamentals and combinations by assuming C(s) point group symmetry. A normal coordinate analysis was also carried out using Simple valence force field. A complete vibrational analysis is presented here for these molecule and results are briefly discussed.     

Vibrational spectra and normal coordinate analysis for cis-diamminetetrachloroplatinum

The normal coordinate analysis of cis-diamminetetrachloroplatinum has been carried out by using a modified Urey—Bradley force field. According to the molecular structure, 45 internal coordinates were established and 33 theoretical vibrational frequencies were calculated. Due to considering the interaction between non-neighbouring stretching vibrations and between bending vibrations and introducing an appropriate set of internal coordinates in the course of calculation, the calculated frequencies agree well with the observed values, with an average difference 3.61 cm⁻¹ between them. The rationality and the reliability of the results are discussed and the questionable empirical assignment of ν(PtCl) in the literature is corrected.     

Vibrational spectra and normal coordinate analysis of diazepam, phenytoin and phenobarbitone

Vibrational spectroscopy is an important tool for the structural investigation of the organic molecules. In the present investigation, a normal coordinate analysis has been carried out on some anti-epileptic drugs, viz. diazepam, phenytoin and phenobarbitone. Diazepam is a derivative of benzodiazepine, phenytoin is a derivative of hydanation and pheonobarbitone is a barbiturate. The infrared spectra of the compounds are recorded in the region 4000-400 cm(-1) and Raman spectra are recorded in the region 3500-50 cm(-1). From the structural point of view, diazepam, phenytoin and phenobarbitone have been assumed to C(s) point group. A systematic set of symmetry coordinates has been constructed for these compounds and Wilson's FG matrix method has been applied for the normal coordinate analysis using general quadratic valance force field. The potential energy distribution is also calculated to check the vibrational band assignments.     

Vibrational spectra,normal coordinate analyses,and molecular configurations of crystalline propionic acid

Temperature dependence of the IR spectra of crystalline propionic acid were examined in the temperature range 242–50 K. The intensities of most absorption bands increased on lowering the temperature, but some bands diminished until they disappeared at temperatures lower than about 120 K. Normal coordinate analyses indicate that the former bands are due to the stable cis dimer and the latter due to the less stable trans dimer which would be produced from the cis dimer by simultaneous proton transfer along two hydrogen bonds.     

Vibrational spectra and normal coordinate analysis of isotopically labelled peroxyformic acid

Infrared spectra of peroxyformic acid (HCOOOH) and the six isotopic modifications H¹³COOOH, HC¹⁸OOOH, DCOOOH, HCOOOD, H¹³COOOD, DCOOOD have been recorded in an argon matrix in the spectral range 200–4000 cm⁻¹. Assignments of the observed absorption lines are presented for the available isotopic species. All fundamental vibrations except one have been identified. A general valence force field has been determined based on the measured vibrational frequencies and on an ab initio MP2/6-31G** force field.     

Vibrational spectra and normal coordinate analysis of p-cresol and its deuterated analogs

I.r. and Raman spectra of p-cresol and its seven deuterated analogs were investigated in dilute solutions of hydrophobic solvents. Assignments of the observed i.r. and Raman bands were made on the basis of isotopic frequency shifts, Raman polarization properties, i.r. intensifies and normal coordinate calculations. The calculated normal frequencies are in good agreement with the experimental ones: the average error below 1700 cm⁻¹ is 3.8 cm⁻¹ for 164 in-plane vibrations and 3.3 cm⁻¹ for 59 out-of-plane vibrations. The calculated vibrational modes may be useful in analysing the vibrational spectra of tyrosine. It is suggested that several doublets due to Fermi resonance and a trio of Raman bands in the 1260-1160 cm⁻¹ region are potential probes for the micro-environments of tyrosine side chains in proteins.     

Vibrational spectra and normal coordinate analysis of 2,2,2-trichloroethanol and 2,2,2-trifluoroethanol

The vibrational spectra of 2,2,2-trichloroethanol and 2,2,2-trichloroethanol and their OD deuterated analogues have been studied in argon, nitrogen and mixed argon—nitrogen matrices. The matrix spectra of the CD₂ deuterated and totally deuterated trifluoroethanol and the Raman and i.r. spectra of the liquid alcohols have also been recorded. A vibrational assignment, supported by normal coordinate analysis, is proposed for both alcohols.     

Vibrational spectra and normal coordinate analyses of the trimethyloxonium and trimethylammonium cations

Raman and i.r. spectra of the compounds (CH₃)₃O⁺ SbCl⁻₆ and (CH₃)₃NH⁺ SbCl⁻₆ are reported and assigned. Normal coordinate calculations support the vibrational assignments for the cations Of C_3v symmetry, and yield force constants k(CO) = 4.05 mdyn·Å⁻¹ and k(CN) = 4.80 mdyn·Å⁻¹ for the trimethyloxonium ion and the trimethylammonium ion, respectively.     

Vibrational spectra and normal coordinate analysis of CF3 compounds: Part XXXV. Vibrational spectra,normal coordinate analysis and electron diffraction studies of (CF3)4Sn

The IR and Raman spectra ofSn(CF₃)₄ have been recorded and analyzed by means of a normal coordinate analysis. The molecular structure has been determined by electron diffraction yielding the geometric parameters (T_d symmetry) τ_a(CF) 133.8(2) pm, τ _a(SnC) 220.1(5) pm and ∠FCF 108.2(2)°. Compared with Sn(CH₃)₄, the SnC bonds are weakened and lengthened by 5.8(6) pm.     

Vibrational spectra and normal coordinate analysis of two isotopomers of the thiosulfate ion

The Raman spectra of ¹⁸O-thiosulfate ion (S₁O⁻²₃) in H₁¹⁸O solution and the IR spectrum of ¹⁸O-sodium thiosulfate in the solid have been obtained. Normal Coordinate calculations fitting all the fundamental wavenumbers of both ¹⁶O and ¹⁸O isotopomers have been carried out transferring the GVFF of the sulfate ion as the starting point and employing a symmetry force field for the least-squares adjustment procedure. A comparison of the results is made with the known force fields for several sulfur compounds.     

Vibrational spectra and normal coordinate analysis of plant growth regulator 1-naphthalene acetamide

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The downshifting of NH₂ stretching wavenumber indicates the formation of intermolecular N–H?O hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.     

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.     

Vibrational spectra and quantum mechanical assignments for 1-nitropropene

The i.r. spectra of cis and trans 1-nitropropene have been recorded in the vapor phase and in various solvents. Theoretical calculations at the Hartree—Fock level with a 3-21G(d) basis set were carried out yielding vibrational frequencies for nitromethane and cis and trans 1-nitropropene. Assignment of fundamentals was assisted by solvent effects on 1-nitropropene. Evidence is obtained for inter-molecular hydrogen bonding.     

Vibrational analysis and normal coordinate analysis of trimethylphosphane

Raman spectra of trimethylphosphine {P(CH₃)₃} as liquid have been recorded with parallel and perpendicular polarization. Vibrational assignments are given by means of a normal coordinate analysis. The skeletal modes of the phosphoruscarbon-core and their interactions with the methyl groups, its force field and potential energy distribution are discussed.     

Vibrational spectra and normal coordinate calculations for dimethyltelluride-d0, -d6 and dimethyltellurium difluoride-d0, -d6

The i.r. (4000-30 cm⁻¹) and Raman (4000-O cm⁻¹) spectra of dimethyltelluride, dimethyltellurium difluoride and their deuterated analogs have been obtained. All the active fundamentals of these compounds except methyl torsions were assigned, assuming a C_2υ molecular symmetry for both the tellurides. Normal coordinate calculations have been made in order to confirm the proposed assignments. The skeletal bond strength of the tellurides together with that of TeF₄ are discussed, using the valence stretching force constants.