IR spectra,conformational lability,and intermolecular interactions in long-chain aliphatic compounds

Investigations of the conformational lability and intermolecular interactions in long-chain aliphatic compounds (LACs), namely, in carboxylic acid derivatives (alkyl- and alkoxybenzoic acids; alkylcyclohexanecarboxylic acids and their completely or partially fluoroalkyl-substituted derivatives), 4-cyano-4-p-alkoxybiphenyls, 4-cyano-4-p-alkylbiphenyls, and cholesterol p-n-butyloxybenzoate are reviewed. Major attention is paid to experimental and theoretical IR spectroscopy data. Differential thermal analysis, polarization microscopy, and X-ray diffraction data are also taken into account. A more detailed treatment is presented on IR spectrum simulation based on data about the conformational lability of molecules and their specific (H-bonding) intermolecular interactions. The first mechanism is responsible for the conformational type of polymorphism in LACs and for the structure of the latter in solid crystal (SC) and liquid crystal (LC) states and in isotropic liquids (ILs). The second mechanism complements the structure-forming aspect of polymorphism in carboxylates, which is due to a rearrangement of hydrogen bond systems in H-complexes during polymorphic transitions to the LC and IL states. Both mechanisms are reflected in IR absorption spectra. A more adequate interpretation is possible in order to explain the many spectral features associated with the structure of LAC polymorphs and their H-complexes if these mechanisms are taken into account.Original Russian Text Copyright © 2004 by L.M. BabkovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 389–397, May–June, 2004.     

Mass spectra of branched long-chain aliphatic alcohols

The mass-spectral behaviour of long-chain aliphatic primary alcohols of the normal, iso-and anteiso-series have been discussed. The mass-spectral fragmentation of individual alcoholic types have been found to be structurally specific. The mass spectra of some deuterio derivatives have shown, however, the complicated nature of the fragmentation processes.     

Chain twisting in long-chain aliphatic compounds and polyethylene

Rate parameters for dielectric relaxation and the thermal properties of long-chain molecular systems are shown to provide evidence for chain twisting at chain lengths shorter than previously suggested. Comparison of the temperatures of maximum absorption at 1 Hz for mechanical and dielectric relaxation suggests that the underlying motion is not the same for the two observed quanties. The evidence for relaxation in polyethylene is shown to be compatible with this suggestion.     

A simple method of calculation of vibrational spectra of long-chain aliphatic compounds and their urea adducts

A semi-quantitative method for calculation of the LCAC's and their urea adducts vibrational spectra based on simple model Hamiltonian on the basis corresponding to excitations of fragments forming the studied system is proposed. A comparison with experimental spectra of LCAC's with different terminal groups and in different phase states is performed. It is shown that the effect of the built-in incommensurability of polymethylene chain and urea lattice in adducts must manifest itself as additional broadening of some bands in the vibrational series of polymethylene chain. The manifestation of possible resonance of “host” and “guest” vibrations has also been analyzed.     

Vibrational spectra and structure of trinitromethane

The vibrational spectrum of trinitromethane was interpreted in terms of the additive interatomic interaction model on the basis of experimental infrared and Raman spectra of HC(NO₂)₃, DC(NO₂)₃, HC(¹⁵NO₂)₃ and normal coordinate analysis. The frequency assignment results were used in discussing its structure. It was shown that the symmetry of trinitromethane is below C₃ in the liquid state.     

Vibrational spectra and structure of isopropylbenzene

Infrared spectra (4,000-400 cm(-1)) and Raman spectra (1,700-40 cm(-1)) of the liquid and two crystalline solids of isopropylbenzene (cumene) and isopropylbenzene-d(12) have been recorded. The spectra indicate that in the liquid and crystalline solids isopropylbenzene exists in planar conformation only (CH bond is in the plane of the benzene ring). An assignment of the observed band wave numbers both isopropylbenzene and isopropylbenzene-d(12) is discussed by comparison with normal mode wave numbers and IR intensities calculated from ab initio 6-31G (d) force fields.     

Spectra and structure of phosphorus-boron compounds : IV. Vibrational spectra of solid trifluorophosphineborane

The Raman spectra of F₃PBH₃ and F₃PBD₃ have been recorded (2500-10 cm⁻¹) of the liquids (−80°C) and solids (−196°C) as well as the infrared spectra (4000-33 cm⁻¹) of the solids. In the spectrum of the solid state many of the ¹⁰B and ¹¹B fundamentals were clearly defined and it was also possible to assign the BH₃ torsional frequency from the infrared and Raman spectra of the solids. A complete vibrational assignment is proposed and a normal coordinate calculation carried out. The force constant of 2.46 mdyn Å⁻¹ for the P-B stretching mode is consistent with the short P-B bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. All of the E modes for the “free” molecule are shown to be split by the site symmetry which indicates that the molecules occupy C_s or C₁ sites. The large number of observed lattice modes is consistent with two or more molecules per primitive cell. The torsional frequency was observed at 224 cm⁻¹ and 167 cm⁻¹ in hydrogen and deuterium compounds in the solid, respectively. These frequencies gave a periodic barrier of 4.15 kcal mole⁻¹ for F₃PBH₃ and 4.31 kcal mole⁻¹ for F₃PBD₃. CNDO/2 calculations have been carried out for F₃PBH₃ and the isoelectronic F₃SiCH₃ molecule in both the staggered and eclipsed forms and the dipole and barrier origins are discussed.     

Vibrational spectra and structure of symmetrical glyoximes

Conclusion Analysis of the vibrational spectra of symmetrical disubstituted glyoximes indicated that these are centrosymmetric molecules which exist, in all likelihood, in the trans-anti configuration.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2348–2351, October, 1986.     

Vibrational spectra and structure of sulfonium nitroimides

Vibrational spectroscopy and x-ray structure analysis have been used to investigate three new types of sulfonium nitroimides: N-nitrosulfylimides, N-nitrosulfoximides, and N,N-dinitrosulfodiimides. Structural parameters have been determined for the molecules , , and .Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2489–2496, November, 1991.     

Vibrational spectra and structure of triphenyltin halides

The solid state IR and Raman spectra of SnPh₃Br do not show any band at 338 cm⁻¹, and there is not C_3ν point group inversion between ν_as SnC₃ and ν_s SnC₃ for SnPh₃X (X  Cl, Br). The presence or absence of a band around 338 cm⁻¹ in the IR spectra of triphenyltin compounds cannot be used to distinguish between pyramidal and planar SnPh₃ groups.     

Vibrational spectra of polyfluoroaromatic compounds containing the azomethine group

Conclusions The replacement of hydrogen atoms of the benzene rings in aromatic azomethines is accompanied by changes in the state of the nitrogen atom and the C=N bond. This is expressed in a shift of the signals in the NMR spectra and in a change in band intensities for the stretching vibrations of multiple bonds in the Raman spectra, but it does not affect the positions of these bands.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 568–575, March, 1984.