Vibrational spectra of 3,5-dimethylpyrazole and deuterated derivatives

The infrared (IR) and Raman spectra of 3,5-dimethylpyrazole have been recorded in the vapor, liquid (melt and solution) and solid states. Two deuterated derivatives, C5H7N-ND and C5D7N-NH, were also studied in solid state and in solutions. Instrumental resolution was relatively low, 2.0 cm(-1) in the IR and approximately 2.7 cm(-1) in the Raman spectra. The solids are made of cyclic hydrogen-bonded trimers. These trimers, present also in chloroform and acetone solutions, give rise to characteristic high absorption IR spectra in the 3200-2500 cm(-1) region, related to Fermi resonance involving nu(NH) vibrations. Bands from trimers are not present in water solutions but these solutions show spectral features similar in several ways to those of the trimer, attributable to solvent-bonded complexes. Evidence of H-bonding interactions with the other solvents is also visible in the high-frequency region. The two very intense bands in the Raman spectra of the solids appearing at 115 and 82 cm(-1) in the parent compound are also connected with a trimer formation. To interpret the experimental data, ab initio computations of the harmonic vibrational frequencies and IR and Raman intensities were carried out using the Gaussian 94 program package after full optimization at the RHF/6-31G* level for the three monomeric compounds as well as for three models of the trimer, with C3h, C3 and C1 symmetry. The combined use of experiments and computations allow a firm assignment of most of the observed bands for all the systems. In general, the agreement between theory and experiment is very good, with the exception of the IR and Raman intensities of some transitions. Particularly noticeable is the failure of the theoretical calculation in accounting for the high intensity of the Raman bands of the solid about 115 and 82 cm(-1).     

Vibrational spectra of some o-substituted benzoic acid derivatives

The use of a semiempirical method based on the application of Group Theory to a previously established geometrical model according to the molecular structure allowed us to carry out the vibrational analysis of infrared and Raman spectra in solid phase of some o-substituted benzoic acid derivatives. Because the influence of the different substituents on the frequency of the ring vibrational normal modes is slight, the study of the ring vibrations independently of the substituent internal vibrations was possible. On this basis a tentative assignment of the ring vibrational normal modes for the o-NH₂, o-CH₃, o-Cl and o-COOH benzoic acids is proposed.     

Vibrational spectra of trinitromethane derivatives

Spectroscopic parameters of trinitromethane derivatives RC(NO₂)₃ (R = F, Cl, Br, I, NC, NF₂, N₃) were determined. Vibrational frequencies and modes were calculated and the assignment of experimental spectra was performed. Spectral features due to the mutual influence of the C(NO₂)₃ group and other atomic groups and particular atoms were revealed.     

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

From an analysis of the IR and Raman spectra and a calculation of the frequencies and forms of the normal vibrations of the nitrotriazoles, conclusions have been drawn on the structure of 3,5-dinitro-1,2,4-triazole and 1-methyl-3,5-dinitro-1,2,4-triazole. The nitro group in position 3 of the triazole ring is located in the plane of the molecule, and that in position 5 is rotated about the CN bond. The spatial nonequivalence of the nitro groups leads to the splitting of the absorption bands in the IR spectra that are characteristic for the anti- and synphase vibrations of the nitro groups.For Communication (II), see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1194–1198, September, 1973.     

Vibrational spectra of 1,3,5-hexatriene and methylated derivatives

The ground state vibrational spectra of E-hexatriene, Z-hexatriene, E,E-heptatriene, E,E,E-octatriene, and E-2,5-dimethyl-hexatriene are reported. For E- and Z-hexatriene complete vibrational assignments, and for heptatriene, octatriene, and dimethyl-hexatriene near-complete assignments are obtained. The effects of terminal and lateral methyl-substitution are compared.     

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 structure of 1,2,4-triazole derivatives

The frequencies and forms of the normal vibrations of the anions of 1,2,4-triazole and 3-nitro-, 3-nitro-5-methyl-, and 3,5-dinitro-1,2,4-triazoles were calculated. The potential energy constants were calculated by solution of the reciprocal spectral problem, and the frequencies in the experimental spectra were assigned to the fundamental types of normal vibrations. It is shown that the nitro groups in the 3 and 5 positions in the anions of the triazoles are located in the plane of the triazole ring. The coordination of the metal in crystalline salts of nitrotriazoles was studied by the methods of vibrational spectroscopy, and an assumption is stated that the most probable position of the metal is near the oxygen atoms of the nitro group along the Me-O-N line. As a result of a theoretical analysis of the vibrational spectra of the anions it was ascertained that equalization of the lengths of the ring CN bonds does not occur during ionization of the covalent triazoles. Calculations by the MO LCAO SCF method are in agreement with the data from vibrational spectroscopy.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1423–1431, October, 1973.     

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

The frequencies and forms of the normal vibrations of 3-nitro-1,2,4-triazole, its 1-deuteroand 1-methyl derivatives, and 1-methyl-3-nitro-5-chloro(bromo)-1,2,4-triazole, which are classified as having C_S group symmetry, were calculated. The potential energy constants were refined by solution of the reciprocal spectral problem, and the frequencies in the experimental spectra were assigned to the principal types of vibrations.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 707–712, May, 1973.     

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 spectra and structure of 1,2,4-trlazole derivatives

The frequencies and forms of the normal vibrations of 3-azido- and 3-azido-5-methyl-1,2,4-triazoles and their 1-deutero-substituted derivatives were calculated, the effect of the geometrical parameters of 3-azido-1,2,4-triazole on the vibrational spectra was investigated, and the most probable three-dimensional model of the molecule was selected. The solution of the inverse spectral problem was effected by the method of least squares, and the potential energy constants of the azidotriazoles were calculated. It is shown that the force constants of the azido group increase and the elastic constants of the ring decrease when an azido group is introduced into the 1,2,4-triazole molecule. The frequencies in the experimental spectra were assigned to the principal types of normal vibrations.     

Heteroatom derivatives of indene: V. Vibrational spectra of benzimidazole

Infrared and Raman measurements for benzimidazole are presented and discussed, including its argon-matrix infrared spectrum. To assist in the assignment, benzimidazole's harmonic force fields for the 321G* and 631G* levels were scaled by scaled factors derived by fitting the respective computed force fields of other indene derivatives to previously reported experimental vibrational frequencies. Comparison to the best set of experimental wavenumbers, usually taken from the matrix, shows mean 321G* and 631G* deviations of 7.0 and 5.8 cm⁻¹ for the planar modes, and 14.0 and 6.8 cm⁻¹ for the nonplanar modes, respectively, with much of the error residing in imino-hydrogen group modes. Standard entropies are derived with the matrix wavenumbers and the methods of statistical mechanics. An attempt to determine standard entropies by calorimetric methods was unsuccessful. The triple-point temperature T_tp and enthalpy of fusion Δ¹_crH_m only are reported.     

Vibrational spectra and structure of some 3-hydroxypyridine 1-oxide derivatives

The vibrational spectra of 3-hydroxypyridine 1-oxide and its derivatives were investigated.On the basis of the assignments of the bands that characterize the OH, N⁺C⁺, and ring C-C bonds, it was established that these compounds exist in the crystalline state as associated zwitterions. It was shown that such associates have a more delocalized -electron system than the monomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–965, July, 1972.     

Rearrangement processes in the mass spectra of some 3,5-dimethylisoxazole derivatives

The mass spectra of isoxazole and some 3,5-dimethylisoxazole derivatives were investigated. Schemes for the formation of the principal rearranged ions are proposed on the basis of a study of the dissociative ionization of labeled compounds. Examples of the effect of electronic and steric factors on the probability of the existence of different channels for disintegration of the molecular ion are presented. It is shown that the formation of an ion with mass 82 during the dissociative ionization of a number of the investigated compounds occurs via different mechanisms as a function of the nature of the substituents in the 4 position of the isoxazole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1336–1340, October, 1972.