Infrared spectra and molecular conformation of butyronitrile and methyl thioacetonitrile

The infrared absorption spectra of two related compounds, butyronitrile (CH₃CH₂-CH₂CN) and methylthioacetonitrile (CH₃SCH₂CN) have been examined in the liquid and solid phases. Vapour phase spectra of butyronitrile have also been recorded. Evidence is given for the existence of two rotational isomers trans and gauche, for both compounds. In both cases the energy difference between the two rotamers appears to be small with the gauche form identified as the low energy conformer for butyronitrile. For methylthioacetonitrile it was not possible to determine the more stable rotational isomer.     

The vibrational analysis of methylarsonic acid,trideuteromethylarsonic acid and their anions

Raman and IR spectra of methylarsonic acid, CH₃AsO₃H₂, trideuteromethylarsonic acid, CD₃AsO₃H₂ and their anions in aqueous solution and the solid state are discussed. Some results of a general valence force field and a Urey-Bradley force field are reported.     

Vibrational spectra of ethyl iodedes

The infrared spectra of CH₃CH₂I, CD₃CH₂I, and CH₃CD₂I of the vapors and the solids at 170°C have been recorded from 4000-200 cm^?1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH₃CH₂X molecules is presented.     

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.     

Schwingungsverhalten des syn- und anti-acetaldoxims: 1. Mitt. Schwingungsspektren

The infrared spectra of CH₃CHNOH, CH₃CHNOD, CH₃CDNOD and CD₃CDNOD have been recorded and studied. On the basis of the symmetry properties the normal vibrations were assigned by comparison.     

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.     

Infrarot-und Raman-Spektren von unvollständig und vollständig deuterierten Tetramethyl-Verbindungen (CH3) n M(CD3)4-n der ElementeM=Si,Ge, Sn und Pb

The infrared andRaman spectra of theM(CH₃)₄ andM(CD₃)₄ species,M=Si, Ge, Sn and Pb, have been reinvestigated. The spectra of the mixed tetramethyl compounds (CH₃)₃ MCD₃,M=Si, Ge, Sn and Pb, and of (CH₃)₂Si(CD₃)₂ and CH₃Si(CD₃)₃ have been recorded in the gaseous (i.r.) and liquid states (Raman). The proposed assignment is supported by a normal coordinate analysis.

     

Vibrational spectra and force constants of Ch3HgI and CD3HgI

The infrared and Raman spectra of CH₃HgI and CD₃HgI were studied in the solid state. All the fundamental wavenumbers are assigned. A general harmonic force field was used as the basis, and the force constants were modified by means of the Jacobian matrix. The force constants fit the observed wavenumbers better than 1 %. The normal coordinates are also given.     

Mid-infrared spectra of methane dispersed in solid neon and argon

We have recorded, in absorption, infrared spectra of samples of methane, CH₄ and CD₄, dispersed at molar fraction 0.0001–0.005 in solid neon, in solid argon and in their equimolar solid mixture in the temperature range 3–21 K and in the spectral domain 5000–500 cm⁻¹ at resolution 0.04–0.2 cm⁻¹. We undertook quantitative fitting of the spectral profiles with components of gaussian and lorentzian shapes. Comparison of our spectra in regions of fundamental modes both ν₃ and ν₄ with published spectra of CH₄ and CD₄ in either crystalline para-dihydrogen or droplets of liquid helium indicates evidence for hindered rotation of CH₄ molecules in Ar but not for rotation of CH₄ or CD₄ in Ne or in a mixture of Ne and Ar. For CD₄ in solid Ar, the evidence for even hindered rotation is ambiguous. We make new assignments of lines to ¹³CH₄ and ¹³CD₄ in their environments in solid Ne and Ar.     

Vibrational and NMR spectra of light and heavy CH3COSH and CD3COSH in relation to tautomerism and hydrogen bonding

The infrared and Raman spectra of CH₃COSH, CH₃COSD, CD₃COSH and CD₃COSD in the liquid and vapor states have been reported and vibrational assignments proposed. The low temperature NMR studies show the presence of hydrogen bonding in this acid. The NMR studies on the neat liquid fail to prove the presence of thion tautomer in thiolacetic acid.     

Schwingungsverhalten des syn- und anti-acetaldoxims: 2. Mitt. normalkoordinatenbehandlung

Normal coordinate calculations on CH₃CHNOH, CH₃CHNOD, CH₃CDNOD and CD₃CDNOD have been carried out applying the general harmonic valence force field. The calculated frequencies of the normal vibrations considered agree satisfactorily with the corresponding values obtained from the spectra. The potential energy distributions have also been calculated; they were used to interpret the behaviour of characteristic vibrations.     

Étude conformationnelle des sulfite et chlorosulfite de méthyle et de leur homologue deutérié

The infrared spectra of (CH₃O)₂S-O, (CD₃O)₂S-O, CD₃OS(-O)C1 and CD₃OS(-O)C1 in pure liquid state and in solution are analyzed in various solvents and at different temperatures. The results obtained show the existence of a conformational equilibrium. The most probable structures of the rotational isomers are presented and the enthalpy of their conversion is calculated.     

Photochemical syn-anti isomerization reactions in N2-hydroxyisocytosines--an experimental matrix isolation and theoretical study

N2-hydroxyisocytosine and 1-methyl-N2-hydroxyisocytosine were studied using a matrix isolation technique combined with infrared absorption spectroscopy. For N2-hydroxyisocytosine isolated in an Ar matrix (at 10 K), two imino-oxo isomers, one with the hydroxyimino =N-OH group directed toward the N1-H group (the form called further anti) and the second with the =N-OH group directed toward N3-H (syn), were observed in the ratio 1.4:1. The syn isomer is converted totally to the anti form after UV (lambda > 295 nm) irradiation of the matrix. A small amount of the N(3)H-hydroxy-amino tautomer of N2-hydroxyisocytosine was also detected in the matrix. This form did not react photochemically. For 1-methyl-N2-hydroxyisocytosine, only the syn form of the imino-oxo tautomer was observed after deposition of the matrix. UV (lambda > 295 nm) irradiation induced a photoreaction converting this isomer into the anti form. After 15% of the starting material had been converted into the product, a photostationary state was achieved, and no further progress of the reaction was observed. Subsequent UV irradiation (lambda > 335 nm) caused a back reaction, leading to a disappearance of the anti form and to the recovery of the initial syn isomer. All isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-31G(d,p) level, where DFT is the density functional theory. Good agreement between the observed and predicted patterns of the spectral lines allowed for reliable identification. The experimental IR spectra were interpreted and discussed. The relative energies of the 12 isomers of N2-hydroxyisocytosine were calculated at the MP2/6-31G(d,p) and MP4//MP2/6-31G(d,p) levels. For six isomers of 1-methyl-N2-hydroxyisocytosine, the calculations were carried out at the MP2/6-31G(d,p) level. The anti form of the imino-oxo tautomer of N-hydroxyisocytosine and the syn form of the imino-oxo tautomer of 1-methyl-N2-hydroxyisocytosine were predicted to be the most stable.     

NMR studies of fluorocarbon diphosphines and oxy- and thio-bisphosphines

Both the diphosphine CH₃CF₃PPCH₃CF₃ and the thio-bisphosphine CH₃CF₃PSPCH₃CF₃ show ¹⁹F and ³¹P NMR spectra indicative of diastereomeric mixtures of d,l and meso isomers. The temperature-dependent reversible interconversions of the isomers have been attributed to the inversion at the phosphorus atom. The equilibrium constants for the isomerization reactions have been measured at various temperatures. The fluorine NMR spectra of the meso and d,l isomers of CD₃CF₃PSPCD₃CF₃ have been analyzed as M₃XX′M₃′ spin systems. Good agreement is found between the observed and calculated spectra. The five-bond fluorine-fluorine coupling constant of the low-field isomer is larger than that of the high-field isomer. The ¹⁹F NMR spectra of (CF₃)₂PP(CF₃)₂, (CF₃)₂POP(CF₃)₂, (CF₃)₂PSP(CF₃)₂, CH₃CF₃PPCH₃CF₃ and CH₃CF₃PSPCH₃CF₃ have been examined over a wide range of temperatures in an attempt to correlate the data to the geometries of these compounds.     

The infrared spectrum and force field of the methyl-ammonium ion in (CH3NH3)2PtCl6

Infrared spectra of the CH₃NH₃⁺, CH₃ND₃⁺, CD₃NH₃⁺ and CD₃ND₃⁺ ions in bis(methylammonium)hexachloroplatinate(IV) have been recorded. The spectra are entirely consistent with the C_3v symmetry reported for the methylammonium ion, at temperatures between room temperature and 90 K. No spectral manifestations of the phase transition, which in (CH₃NH₃)₂PtCl₆ has been reported to take place at 125 K, were observed. Assignments of the infrared-active fundamentals have been made for each ion and a normal-coordinate analysis has been performed using the observed fundamental frequencies. Comparison with the infrared spectra of other methylammonium salts shows that hydrogen bonding in (CH₃NH₃)₂PtCl₆, if present, is weak.     

Vibrational spectra and normal coordinate calculations for (CH3)3GECN and (CD3)3GECN

Infrared spectra of (CH₃)₃GeCN and (CD₃)₃GeCN have been obtained over the range of 4000–100 cm^?1 from solutions of benzene and dichloromethane, and solid films deposited on windows at liquid nitrogen temperature. Raman spectra have been photographed in dichloromethane solution. Assignments for all fundamentals except the internal torsions have been made, and normal coordinate calculations carried out by a symmetry force field to confirm the proposed assignments.     

Association of tert-butyl alcohol: a matrix infrared study

Infrared spectra of (CH₃) ₃COH, (CH₃)₃COD, (CD₃)₃COH and (CD₃)₃COD have been studied in the liquid and solid states, in CCl₄ and CS₂ solutions, and in argon, krypton and nitrogen matrices. The Raman spectra of the solids and of CCl₄, and H₂O solutions have been recorded. The matrix infrared results show that in the matrices tert-butyl alcohol has two well-defined dimer associates, both of which seem to have an open-chain structure. A network is proposed for the higher associates. The relative strengths of the protium and deuterium bonds are discussed in terms of the monomer hydroxyl-stretching frequencies and the Δv shifts. Association characteristics of the most important fundamental bands in several spectra are given.     

Theoretical study of the force field and vibrational assignments of acetamide and deuterated analogues

The complete harmonic force constants of acetamide have been evaluated by ab initio calculations at the Hartree-Fock level with the 4–31G(d) basis set. The force field was scaled to compensate for the systematic overestimations of the Hartree-Fock-level force constants by empirical factors using the matrix isolation IR spectra of CH₃CONH₂ and CD₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃COND₂, cis-CH₃CONHD and trans-CH₃CONHD. The effect of cis/trans isomerism of CH₃CONHD on the fundamental bands was well reproduced by the calculations. The fundamental vibrations were also predicted for CD₃COND₂, cis-CD₃CONHD and trans-CD₃CONHD.     

Photochemical syn-anti isomerization reaction in N4-hydroxycytosine. An experimental matrix isolation and theoretical study

Infrared spectra of N4-hydroxycytosine isolated in argon and nitrogen low-temperature matrixes are reported. The compound was found to adopt the syn structure of the imino-oxo tautomeric form exclusively. A photoreaction (lambda > 250 nm) converting this form into the anti isomer was observed. The reaction is reversible and leads to a photostationary point. The initial infrared spectrum and the spectrum of the photoproduct were assigned to the syn and anti isomers, respectively. This assignment is based on a close agreement between the experimental spectra and the spectra theoretically simulated at the DFT(B3LYP)/6-31++G** level of theory.     

Determination of force fields for formaldehyde,acetaldehyde and acetone by the CNDO/force method

CNDO/Force calculations have been done for formaldehyde, acetaldehyde and acetone, and the theoretical force fields evaluated. Experimental force fields are obtained from vibrational frequencies using the least-squares refinement method. The initial force fields considered are based on the bending and interaction force constants obtained from the CNDO/Force calculations and the stretching force constants transferred from chemically related molecules. Vibrational frequencies of H₂CO, D₂CO, HDCO, H₂¹³CO and D₂¹³CO for formaldehyde, CH₃CHO, CH₃CDO, CD₃CHO, CD₃CDO and CH₂DCHO for acetaldehyde, and CH₃COCH₃ CD₃COCH₃ and CD₃COCD₃ for acetone are employed in the force field refinements. The final force fields obtained are found to be reasonable with respect to the diagonal and interaction force constants.