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 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 diacetylene and its deuterated species

Infrared and Raman spectra of diacetylene-d₀, -d₁, and -d₂ have been recorded and a complete vibrational analysis is proposed for each of these three species.     

Vibrational spectra of hypophosphite ion and its deuterated species

The infrared and Raman spectra of the H₂PO₂^?, HDPO₂^? and D₂PO₂^? ions have been measured in aqueous solutions. The assignment of bands to the fundamental vibrations proposed is based on experimental tests, band polarisation measurements, application of all known isotopic rules and the construction and analysis of all the physically admissible assignments. The thermodynamic functions of the studied ions are calculated in the rigid rotator and harmonic vibrator approximation.     

Vibrational spectra of alkali metal peroxoborates

Raman and i.r. spectra of solid Na₂[B₂(O₂)₂(OH)₄]·6H₂O (normal, ¹⁰B, ¹¹B, and ²H-substituted), Na₂[B₂(O₂)₂(OH)₄]·nH₂O (n=4, 0), Li₂[B₂(O₂)₂(OH)₄] and M^I₂[B₂(O₂)₂(OOH)₂(OH)₂] (M^I= K, Rb, Cs) are reported and the vibrational modes assigned.     

Vibrational spectra of the hydrazides of (tetrazol-1-yl)- and (tetrazol-2-yl)acetic acids and their deuterated analogs

The hydrazides of (tetrazol-1-yl)- and (tetrazol-2-yl)acetic acids and their deuterated analogs are investigated by means of IR spectroscopy. On the basis of the data obtained, assignments in the vibrational spectra of the isomers are made.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 72–76, January, 1991.     

Vibrational spectra and the structures of alkali metal caprolactamates

Based on analysis of the IR and Raman spectra of Na and K caprolactamates it has been established that these exist not in two forms (lactamic and lactimic), as previously proposed, but rather in one form, intermediate in structure between these two forms, in which the negative charge is delocalized uniformly across the amide bond. It has also been shown that spectral bands at 1560 and 1400 cm–1 for these salts correspond to the antisymmetric and symmetric stretching vibrations of this bond.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 335–339, February, 1990.     

Vibrational spectra of phenyltriethoxysilane, phenyltrimethoxysilane and their sol-gels

Raman and infrared spectra of phenyltriethoxysilane and phenyltrimethoxysilane have been recorded. These silane coupling agents (SCAs) have been used as precursors to prepare sol-gels using acid or base as catalyst under different solution conditions. From the vibrational spectroscopic identification, it was found that the major sol-gel products obtained from different catalysts and different solvents were essentially the same. Vibrational assignments for the SCAs, sol-gel and xerogel have been made based on the group frequencies, the spectral variation collected at different physical and chemical states and the previous spectroscopic studies of similar molecules. The compositions of xerogels after thermal treatments at different temperatures have been analyzed and identified by using infrared spectroscopic method along with thermal gravimetric analysis. Results from the experimental treatments for the xerogels indicated that the xerogel baking at 118 degrees C served to evaporate the sample moisture, the curing at 225 degrees C helped to complete the condensation reaction, and the treatment at 600 degrees C caused the decomposition of the organic group but the siloxane net-work remained essentially unchanged.     

Vibrational spectra and molecular force field of N-methylpyridinium ion and some deuterated derivatives

The vibrational spectra of N-methylpyridinium iodide and three of its selectively deuterated derivatives have been recorded in the crystalline as w     

Vibrational analysis of l-alanine and deuterated analogs

Raman spectra of the polycrystalline l-alanine analogs CH₃CH(NH⁺₃)COO^?, CH₃CH(ND⁺₃)-COO^?, CD₃CD(NH⁺₃)COO^?, and CD₃CD(ND⁺₃)COO^? have been obtained. A normal coordinate analysis is carried out based on the experimental frequencies of the four isotopic analogs and a 34 parameter valence-type force field defined in terms of local symmetry coordinates. The final refinement, in which five stretching force constants are constrained to fixed values obtained from bond length data, results in an average error of 7 cm^?1 (0.9%) for the observed frequencies of the four isotopically substituted molecules. Band assignments are given in terms of the potential energy distribution for local symmetry coordinates. For non-deuterated l-alanine, the vibrations above 1420 cm^?1 and below 950 cm^?1 may be described as localized group vibrations. By contrast, the eight modes in the middle frequency range, viz. the three skeletal stretching, the COO^? symmetric stretching, one NH⁺₃ rocking, the symmetric CH₃ deformation, and the two methyne CH deformation vibrations, are very strongly coupled to one another. Some decoupling appears to take place in the perdeutero molecule, and all but five modes can be described as localized group vibrations.     

Vibrational spectra of tetramethyleyclobutane-1-one-3-thione and the fully deuterated derivative

Raman and i.r. spectra of tetramethylcyclobutane-1-one-3-thione (TMCBOT) and the fully deuterated derivative TMCBOT-_d¹² have been recorded. A fairly complete set of vibrational frequencies and assignments are given for the two molecules. The CO stretching mode was observed as a very strong Fermi doublet in the infrared spectrum of TMCBOT at 1811/1782 cm⁻¹. For TMCBOT-d₁₂ a similar doublet was observed at 1808/1775 cm⁻¹. The CS stretching mode was assigned to bands at 1303 cm⁻¹ for TMCBOT and 1307 cm⁻¹ for the deuterated molecule.     

Vibrational spectra and structure of mixed alkali borotungstate glasses: Evidence of mixed alkali effect

Mixed alkali borotungstate glasses with xLi₂O–(30 − x)Na₂O–10WO₃–60B₂O₃ (0 ≤ x ≤ 30) composition were prepared by melt quench technique. FT-IR and Raman spectroscopic studies were employed to investigate the structure of all the prepared glasses. Acting as complementary techniques, both IR and Raman measurements revealed that the network structure of the present glasses mainly based on BO₃ and BO₄ units placed in different structural groups. Raman spectra confirm the IR results regarding the presence of tungsten ions mainly as WO₆ groups. In the present work, the mixed alkali effect (MAE) has been investigated in the above glass system using FTIR and Raman studies.     

Formation and thermal stability of selenites and hydrogen selenites of samarium

The solubility isotherm of the Sm₂O₃-SeO₂-H₂O system was studied at 100°C. The two compounds obtained in the three-component system were identified by the Schreinemakers method as well as by chemical, thermoanalytical and X-ray diffraction analyses after their isolation in pure state.     

Vibrational spectra and a potential function for 3-chlorocyclopropene and its various deuterated modifications

I.r. and Raman spectra have been obtained for 3-chlorocyclopropene and 3-chlorocyclopropene-d₃ under a variety of experimental conditions. For mixtures of the two d₂ isotopic species and of the two d₂ isotopic species, only infrared spectra have been recorded. The pattern of gas-to-condensed-phase frequency shifts is interpreted as evidence of hydrogen bonding for the CH hydrogen atoms. A complete assignment of the vibrational fundamentals for the d₀ and d₃ species is derived from the spectra. For the d₀ species these frequencies (in cm⁻¹) are: (a′) 3171, 3029, 1633, 1266, 1141, 913, 713, 591, 345; (a″) 3140, 1034, 1017, 866, 840, 349. With guidance from normal coordinate calculations 59 of the 60 fundamentals for the d₁ and d₂ species are assigned. The full set of 89 observed frequencies has been used to fit an 18-parameter valence-type potential function. In comparison with the force constants for CC and CC stretching of cyclopropene and 3,3-difluorocyclopropene, the CC force constants of 3-chlorocyclopropene show changes similar to those expected for a substitution of a single fluorine atom. This finding is consistent with a σ-acceptor role for the mechanism of the interaction of fluorine and chlorine atoms with the cyclopropene ring system.     

Vibrational spectra of nucleic acid bases and their Watson–Crick pair complexes

The vibrational spectra of the nucleic acid bases adenine, thymine, guanine, and cytosine are calculated in the frame of density functional theory (DFT). In particular we use the Kohn–Sham scheme with gradient corrections for exchange and correlation to determine normal modes, frequencies, and intensities. The DFT results are found to be in good agreement with the experiment. Our computations provide assignments for IR, Raman, and neutron inelastic scattering spectroscopies; yield characteristic vibrational fingerprints of each compound for its identification in larger systems; and show general vibrational trends of nucleic acids. The Kohn–Sham scheme is further applied to obtain the spectra of the Watson–Crick pairs adenine-thymine and guanine-cytosine. A large number of monomeric vibrations are recognized in dimers; characteristic vibrations of pairs, which are mainly attributed to hydrogen bridges, are quantified according to changes in normal modes and frequency shifts. Binding and zero-point vibrational energies are analyzed to establish the stability of the complexes and discuss the quality of the energetic calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 511–530, 1999     

Vibrational spectra of potassium hydrogen 3,4 furandicarboxylate and intramolecular H-bond

I.r. and Raman spectra of potassium hydrogen 3,4 furandicarboxylate are presented. An assignment of the band is proposed and the details of the hydrogen bond bonds are discussed by analogy with potassium hydrogen maleate. Anharmonic coupling between ν_as, OHO and ν_s OHO is found in the combination band at about 1000 cm⁻¹.     

Vibrational spectra of potassium hydrogen 2,3-furandicarboxylate and intramolecular H-bond

Infrared and Raman spectra of KHFur 2,3 and KDFur 2,3 are presented. An assignment of the bands is given which is in good agreement with previous results concerning acid salts possessing intramolecular hydrogen bonds. The ν_as OHO participation was observed at 670 and 520 cm⁻¹, absorption bands of medium intensity. The absence of a more pronounced broadening might be explained by assuming an anharmonic coupling between the ν_as OHO and the ν_s OHO modes, resulting in a combination band at 1000 cm⁻¹.     

Vibrational spectra of 3,5-dialkylbenzoic acid derivatives

A comparative vibrational spectra study of 2- and 4-CH₃, −NO₂ and Br-derivatives of some 3,5-dialkylbenzoic acids (R:-Me, −Et, −Prⁱ, −Bu^t) is carried out. We propose an explanation of its molecular structure.     

Separation of organic compounds and their deuterated analogs by preparative gas chromatography

Conclusions Using the circulation GLC method we were able to effect the preparative separation of some ordinary and fully deuterated products with an efficiency that is comparable to that achieved using capillary chromatography and exceeds 40 thousand theoretical plates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimieheskaya, No. 7, pp. 1627–1629, July, 1977.