Metallomethanes: XIII. Vibrational spectra and force fields of cyanomercuriomethanes

Vibrational spectra with assignments and results of normal coordinate calculations for cyanomercuriomethanes CH_4−n(HgCN)_n (2 ≤ n ≤ 4) are discussed. The valence force constants of the central CHg bonds are 2.149, 1.944, and 1.798 N cm⁻¹,while those of the HgCN bonds are 2.204, 2.123, and 2.162 N cm⁻¹, for n = 2, 3 and 4, respectively. All these force constants are lower than the corresponding constants for methylmercury cyanide (2.445 and 2.379 N cm⁻¹). The overall behaviour of these force constants as a function of the degree of mercuration n is quite similar in both the cyanomercuriomethanes CH_4−n(HgCN) and methylmercuriomethanes CH_4−n(HgCH₃)_n series with the difference that there are variations in the constants at higher values in the former series. The potential energy distributions indicate that the valence vibrations of the CH, CN, and HgCN bonds are almost independent of all other vibrations, which in turn are more or less strongly coupled.     

Metallomethanes: XII. Vibrational spectra and force fields of methylmercurimethanes

The vibrational spectra data, the assignments, and the results of normal coordinate calculations for CH_{4 − n}(HgCH₃)_n molecules (2 ⩽ n ⩽ 4) are reported. The central CHg valence force constants are 1.870, 1.653, and 1.582 N cm⁻¹ while the terminal ones are 2.121, 2,101, and 2.160 N cm⁻¹ for n = 2, 3 and 4, respectively. The latter values are 12, 21, and 27% higher than the central CHg force constants, but all of them are substantially lower than those in dimethylmercury (2.379 N cm⁻¹). These findings can be accounted for in terms of increasing shift of electron density towards the periphery of these molecules and increasing non-bonded metal-metal interaction. The nature of the normal modes is discussed.     

Vibrational spectra and harmonic force fields of pyrrolidine derivatives: comparison between HF, MP2 and DFT force fields

Infrared and Raman spectra are reported for the isotopic species of pyrrolidine-d₀ (PY) and -d₁ and for N-methylpyrrolidine-d₀ (NMP), -d₂, -d₃ and -d₈. A complete assignment of the experimentally observed bands to normal modes is presented and discussed in particular in the CH/CD stretching region. The molecular structures and harmonic force fields were calculated ab initio at the Hartree–Fock (HF), the second order Møller–Plesset (MP2) and the density functional theory (DFT) level with the 6-31G* basis set. The force fields were fitted by use of 7 (PY) and 4 (NMP) independent scale factors. The spectra calculated with the DFT force fields are in better agreement with the experiment than those calculated by the MP2 and HF force fields. Though some scaled fundamental frequencies show larger deviations from the experimental ones, the mean percentage deviations of calculated frequencies from experimental fundamentals are less than 2.6% for all isotopic species of PY and NMP under study. The results indicate that density functional theory is a reliable tool to get a deeper insight in the assignment of vibrational spectra and the nature of normal modes of pyrrolidine derivatives.     

Study of the electronic spectra of sydnones and sydnoneimines

The absorption spectrum of 3-methylsydnone and the luminescence spectra of 3-methyl- and 3-phenylsydnone and 3-methylsydnoneimine hydrochloride were interpreted on the basis of calculations by the Pariser-Parr-Pople method with allowance for a correction for the solvent effect.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 53–55, January, 1976.     

Vibrational spectra and force constants ofS-methyl-N,N-dimethyldithiocarbamate

The IR and Raman spectra ofS-methyl-N,N-dimethyldithiocarbamate were studied in different phase states. The frequencies and vibration modes of normal vibrations were analyzed, and the erroneous assignments made in some previous works were corrected. The force constants of the molecule were estimated using the model of the generalized valenceforce field.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1108–1110, June, 1995.This work was carried out with partial financial support from the International Science Foundation.     

Short-wave band in the electronic spectra of sydnones and sydnonimines

A new absorption maximum was observed in the UV spectra of sydnones and sydnonimines at 200 nm, and the effect of substituants and solvents on its position was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 464–465, April, 1972.     

Vibrational spectra and force field of terephtalonitrile

The IR and Raman spectra of the two molecules terephtalonitrile and terephtalonitrile-¹⁵N were recorded to permit the general assignment of the vibrational bands observed, in agreement with a D_2h symmetry for these molecules. The general quadratic force field was calculated by the semi-empirical MINDO/3 method from an optimized geometry obtained by the same method. The resulting force field was refined by employing the experimental vibrational frequency data of the two molecules and those of terephtalonitrile-d₄. The final differences between the calculated end experimentally observed frequencies for B_2g and B_3u terephtalonitrile species were within the range ± 0.1 cm⁻¹.     

Vibrational spectra and force field of dimethylphosphines

Vibrational spectra in the range 200–3000 cm^?1 are reported and assigned for the species (CH₃)₂PH, (CH₃)₂PD, (CD₃)₂PH, (CD₃)₂PD, CH₃CD₃PH and CH₃CD₃PD. The spectra in the range 1020–500 cm^?1 are complicated due to the coupling between δPH, ?Me and the skeletal modes of the molecule. Interpretation is only possible through a force field which is markedly different from an earlier one of dimethyl sulphide. This force field predicts uncoupled δPH frequencies of 835 (a) and 909 cm^?1 (a), couples PH bending largely to out-of-skeletal plane methyl rocking (?_i) and includes a low p¦¦(a) bending constant, a high skeletal bending constant and unusual signs for two interaction constants. In the crystalline phase at 78 K, the two methyl groups are non-equivalent.     

Vibrational and electronic spectra of synthetic moolooite

The infrared and Raman spectra of synthetic moolooite, Cu(C2O4).nH2O, were recorded and analyzed on the basis of its structural characteristics and by comparison with related species. The thermogravimetric analysis of the investigated samples show that the water content n, was equal to 0.2. The electronic (reflectance) spectrum of the complex was also recorded and briefly discussed.     

The mass spectra of sydnones

The mass spectra of thirty sydnoes have been interpreted; the types investigated include 3-aryl, 3-alkyl-, substituted 3-alkylsydnones; and bis sydnones. A characteristic fragmentation mode involves initial loss of NO and CO from the molecular ion, but peaks corresponding to alkylcarbonium ions dominate the spectra of 3-alkylsydnones; a cyclic mechanism is suggested for weak transitions involving loss of sydnone neutral molecule from the molecular ion. A mechanism is proposed for loss of chlorine radical from the molecular ion of 3-(2,4-dichlorophenethyl)sydnone. An unusual feature in the mass spectrum of trimethylenebis sydnone is rationalised on the basis of a precursor 1,2,3-oxadiazole ion. The effect of substituents in the aryl ring on the fragmentation of 3-arylsydnones is discussed.     

Vibrational spectra and structures of 1,2,4-triazole derivatives

The frequencies and forms of the normal vibrations of a number of azido derivatives of 1,2,4-triazole [3-bromo-5-azido-(I), 1-methyl-3razido-(II), and 3-azido-5-nitro-1,2,4-triazole (III)] were calculated. The inverse spectral problem for the parameters of the azido group was solved by the method of least squares. A similar method was used to calculate the potential energy constants of the triazole ring with the aid of data on the force fields of the previously investigated nitrotriazoles. It is shown that the introduction of electron-donor or electron-acceptor substituents in the triazole ring does not affect the force constants of the CN and NN bonds of the azido group. Transmission of the electronic effects in the ring as a function of the nature and position of the substituent was investigated.See [1] for communication V.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 839–842, June, 1977.     

Vibrational spectra and structures of 1,2,4-triazole derivatives

The vibrational spectra of 1,2,4-triazole and its 3-chloro and 3-bromo derivatives were calculated for the C_S point symmetry group. The potential energy constants were computed, and it is shown that the force field of the triazole ring has the additivity property; i.e., it remains practically constant when electron-acceptor groups such as chlorine and bromine are introduced into the 3 position. The force constants of interaction of the valence and angular coordinates of the ring have high values; this is a characteristic of the considerable rigidity of the triazole ring. The fundamental frequencies in the experimental spectra were assigned on the basis of an analysis of the calculated forms of the normal vibrations.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1567–1570, November, 1972.     

Vibrational and electronic absorption spectra of some trisubstituted benzenes

Despite our studies on the Π* ← Π systems in some trisubstituted benzenes, the available data are limited, especially concerning two heavy and one light or one heavy and two light substituents. We therefore report and interpret the vapour phase electronic absorption, infrared and Raman spectra of 1-bromo-2,4-difluoro-, 1-bromo-3,4-difluoro-, 1-bromo-3,5-difluoro-, 1,3-dichloro-2-fluoro- and 1,3-dichloro-4-fluoro-benzenes.     

Structure, force fields, and vibrational spectra of cerium tetrahalides

The geometrical structure, force fields, and vibrational spectra of CeX₄ (X = F, Cl, Br, I) were investigated by second, third, and fourth order Möller-Plesset perturbation theory, CISD+Q configuration interaction method, and the CCSD(T) coupled cluster method. Calculations on CeF₄ were also performed by multiconfiguration second order perturbation theory MCQDPT2/CASSCF. The wave function of the ground state of CeX₄ molecules was found to be appreciably non-one-configurational; this property increases from cerium fluorides to iodides and leads to the divergence of the series of Möller-Plesset perturbation theory. The calculated data point to a tetrahedral equilibrium nuclear configuration in CeX₄ molecules. The energy barriers to the inversion of the tetrahedral CeX₄ molecules via the square configurations are high enough, 74–89 kJ/mol. The calculated vibration frequencies, effective internuclear distances, and mean amplitudes of nuclear vibrations in CeF₄ agree with IR and Raman spectroscopic and high-temperature gas-phase electron diffraction data.