Vibrational analysis of substituted phenols: part II. Transferability of valence force constants

A zero-order normal coordinate analysis was made for the in-plane and out-of-plane vibrations of 2,6-dimethylphenol, 2,3-dimethylphenol, 3,5-dimethylphenol, 2,6-dichloro-4-nitrophenol, 2,4-dichloro-6-nitrophenol, 3-chloro-4-hydroxy-5-methoxybenzaldehyde, 3-bromo-4-hydroxy-5-methoxybenzaldehyde and 3-iodo-4-hydroxy-5-methoxybenzaldehyde and for the in-plane vibrations of 2-amino-4-nitrophenol by transferring the force constants obtained beforehand. The transferability of the force constants was demonstrated by the good agreement between the observed and calculated frequencies. On the basis of calculated potential energy distributions and eigenvectors, several assignments suggested by earlier workers have been revised.     

Vibrational analysis of mononitro substituted benzamides, benzaldehydes and toluenes. Part I. Vibrational spectra, normal coordinate analysis and transferability of force constants of nitrobenzamides, nitrobenzaldehydes and nitrotoluenes

The Raman and Fourier transform infrared (FTIR) spectra of p-, m- and o-nitrobenzamides, p-, m- and o-nitrobenzaldehydes and p-, m- and o-nitrotoluenes were recorded. Raman polarisation measurements were made for the liquid samples. A normal coordinate analysis was carried out for both in-plane and out-of-plane vibrations of these molecules using 111-parameter modified valence force field. The force constants were refined using 316 frequencies of nine molecules in an overlay least-square technique. The reliability of the force constants was tested by making a zero-order calculation for nine related molecules. Unambiguous vibrational assignments of all the fundamentals were made by using the potential energy distributions and eigen vectors.     

Vibrational analysis of tertiary alkyl bromides

Infrared spectra have been obtained for 2-bromo-2-methylpentane and 3-bromo-3-methylpentane. Both compounds exist in T_HHH and T_CHH conformations. Normal coordinate calculations were made for these two compounds and for 2-bromo-2-methylbutane, using the 44-parameter modified valence force field that was used for tertiary chlorides. Fifteen force constants were adjusted to fit 169 frequencies below 1500 cm^?1 of six molecules (two each for the three named compounds) with an average error of 5.6 cm^?1. Vibrational assignments are presented.     

Vibrational analysis of hydroxyacetone

In order to be able to fully understand the vibrational dynamics of monosaccharide sugars, we started with hydroxyacetone CH2OHCOCH3, and glycolaldehyde CH2OHCOH, which are among the smallest molecules that contain hydroxyl and carbonyl group on neighboring carbon atoms. This sterical configuration is characteristic for saccharides and determines their biochemical activity. In this work vibrational analysis of hydroxyacetone was undertaken by performing the normal coordinate analysis for glycolaldehyde first, and transferring these force constants to hydroxyacetone. The observed Raman and infrared bands for 90 wt.% solution of hydroxyacetone in water (acetol) were used as a first approximation for the bands of free hydroxyacetone. The number of observed Raman and infrared bands for acetol exceeds the number of calculated values for the most stable hydroxyacetone conformer with Cs symmetry, which suggests more than one conformer of hydroxyacetone in water solution. In particular, there are two bands both in infrared (1083 and 1057 cm(-1)) and in Raman spectrum (1086.5 and 1053 cm(-1)) that are assigned to the CO stretching mode and this is one of the indicators of several hydroxyacetone conformers in the solution. Additional information was obtained from low temperature Raman spectra: at 240 K a broad asymmetric band centered around 280 cm(-1) appears, suggesting a disorder in the orientation of hydroxyl groups. Glassy state forms at approximately 150K. The broad band at 80 cm(-1) is assigned to frozen torsions of hydroxymethyl groups.     

Vibrational analysis of flavin derivatives: Normal coordinate treatments of lumiflavin

Normal coordinate calculations were carried out for lumiflavin (Lf) and isotope- or methyl-substituted derivatives of it; [3-ND]Lf, [3-NMe]Lf, [2-¹³C]Lf, [4a-¹³C]Lf, [5-¹⁵N]Lf, [1, 3-¹⁵N]Lf and [1, 3, 5-¹⁵N]Lf. Using 69 force constants of the modified local symmetry force field, the observed resonance Raman bands and i.r. bands of these molecules could be assigned to the normal modes. The vibrational modes are represented in terms of the calculated atomic displacement vectors.     

Vibrational spectrum, conformational stability, structural parameters and ab initio calculations of dimethylaminodifluorophosphine

From analysis of the infrared and Raman spectra along with support from the ab initio predictions it is concluded that there is only one stable conformer of dimethylaminodifluorophosphine, (CH(3))(2)NPF(2), in the gaseous and liquid phases which has a planar PNC(2) moiety with C(s) symmetry. The adjusted r(0) structural parameters have been obtained by combining the MP2(full)/6-311+G(d) predicted values with the previous reported rotational constants for four isotopomers obtained from previously reported microwave studies. The difference in the two NC distances is 0.002A whereas, these two parameters were previously assumed to have the same values from the microwave and electron diffraction studies but a reported difference of 0.025A from the structural parameters of the crystal. The adjusted r(0) heavy atom distances and angles are: r(PF)=1.593(3); r(NP)=1.654(3); r(NC(i))=1.455(3); r(NC(o))=1.453(3) A; angleFPF=93.5(5); angleNPF=100.8(5); angleCNC=116.0(5); angleC(i)NP=124.1(5); angleC(o)NP=120.0 degrees . The planar bonding around the nitrogen atom is consistent with the previously reported structural information from the microwave study but differs from the slightly pyramidal bonding obtained in the electron diffraction investigation. To support the vibrational assignment MP2(full) ab initio calculations with the 6-31G(d) basis set were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values, infrared band contours, and centrifugal distortion constants. Vibrational assignments are given for (CH(3))(2)NPF(2) and (CD(3))(2)NPF(2) and comparisons are made with the predicted intensities, frequencies and centrifugal distortion constants. Frequencies of some of the lattice modes are reported from both the infrared and Raman spectra with suggested assignments based on the factor group symmetry of the crystal of D(2h)(16) (Pnma) with four molecules per primitive cell. These results are compared to the corresponding quantities of some similar molecules.     

Vibrational analysis of tertiary alkyl chlorides

Vibrational spectra were obtained for 2-chloro-2-methylpentane, 3-chloro-3-methylpentane, 2-chloro-2-methylhexane, and 3-chloro-3-methylhexane. All four compounds exist in T_HHH and T_CHH conformations in the neat liquid, and the T_HHH' conformer of the last named compound also seems to be present. Only the T_HHH conformer is present in the crystalline state of the two pentanes, but the hexanes could not be made to crystallize and both conformers were present in the solid. A 44-parameter modified valence force field was used in normal coordinate calculations, with fifteen force constants being adjusted to fit 188 assigned frequencies below 1500 cm^?1 of six molecules (two conformers each of 2-chloro-2-methylbutane, 2-chloro-2-methylpentane, and 3-chloro-3-methylpentane). The resulting force constant values were used in zero-order calculations of the two hexanes as an aid in interpreting vibrational spectra for those compounds.     

Vibrational analysis of substituted nitrobenzenes. I—Vibrational spectra,normal coordinate analysis and transferability of force constants of some chlorinated nitrobenzenes

The Raman and Fourier transform infrared spectra of 2,3-dichloro-, 2,4-dichloro-, 2,5-dichloro-, 3,4-dichloro-, 3,5-dichloro-, 2,3,4-trichloro-, 2,4,5-trichloro-, 2,4,6-trichloro-, 2,3,5,6-tetrachloro- and pentachloronitrobenzene were recorded. Raman polarization measurements were made wherever possible. A normal coordinate analysis was carried out for both the in-plane and out-of-plane vibrations of these molecules using a 59-parameter modified valence force field. The force constants were refined using an Overlay least-squares technique employing 352 frequencies of 10 molecules. The reliability of the force constants so obtained was tested by making a zero-order calculation for p-, m- and o-dinitrobenzenes, 1-fluoro-, 1-chloro- and 1-bromo-, 2,4-dinitrobenzenes, 2,4-difluoro- and 2,5-difluoro- and 2,5-dibromonitrobenzenes. Unambiguous vibrational assignments of all the fundamentals were made using the potential energy distribution and eigen vectors.     

Vibrational analysis of ethyl and n-propyl fluorides

Infrared spectra of n-propyl fluoride in the gas and solid states were obtained that confirm the presence of two molecular conformations in the gas and unannealed solid. Only one conformation identified as the gauche form is present in the annealed solid. Raman spectra were obtained for the solid. Normal coordinate calculations were made simultaneously for ethyl fluoride, gauche n-propyl fluoride, and trans n-propyl fluoride, and the resulting force constants and vibrational assignments are given.     

Vibrational spectrum of 3-methyl and 4-methylpyridine

The assignments of the vibrational spectra of the 3-methyl and 4-methylpyridine molecules have been carried out following the SQMFF methodology (scaled quantum mechanical force field). The theoretical frequencies have been obtained by calculating the RHF/3-21G force field, using the scale factors for pyridine and 2-methylpyridine and are correlated in a satisfactory manner with the frequencies recorded in the IR and Raman of these methyl derivatives.     

Vibrational spectra and normal co-ordinate analysis of 2-aminopyridine and 2-amino picoline

The Fourier transform infrared (FT-IR) and Raman (FT-R) spectra of 2-aminopyridine and 2-amino picoline were recorded and the observed frequencies were assigned to various modes of vibration in terms of fundamentals by assuming Cs point group symmetry. A normal co-ordinate analysis was also carried out for the proper assignment of the vibrational frequencies using simple valence force field. A complete vibrational analysis is presented here for the molecules and the results are briefly discussed.     

Vibrational spectra, conformations, and force constants of bis(dimethylamino)chlorophosphine and 2-chloro-1,3-dimethyl-1,3,2-diazaphospholane

Conformational analysis of the molecules of bis(dimethylamino)chlorophosphine and 2-chloro-1,3-dimethyl-1,3,2-diazaphospholane was carried out by the molecular mechanics method. According to calculations, both compounds are conformationally homogeneous, which is in agreement with the data of vibrational spectroscopy. The structural parameters found were used to calculate the frequencies and modes of normal vibrations, to analyze the IR and Raman spectra, and to estimate force constants for both diaminophosphines. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 391–394, March, 1998.     

Vibrational spectra of Hg3TeO6 and Hg2TeO5

The infrared and Raman spectra of the crystalline hexaoxotellurates Hg3TeO6 and Hg2TeO5 were recorded and discussed on the basis of a site symmetry analysis derived from known structural data. Approximate values for the Te-O bond force constants are reported and some comparisons with related species are made.     

Vibrational spectra of imidazoline-2-thione and imidazoline-2-one

Raman and infrared spectra of imidazoline-2-thione (IMZT) and imidazoline-2-one (IMZO) have been recorded. Normal coordinate analyses have been performed for all the fundamental vibrations of IMZT, IMZT-d₂ and IMZO employing a Urey—Bradley potential function supplemented with valence type force constants for the out of plane modes. The results of the vibrational analyses are discussed in relation to the assignments in related molecules. The vibrational assignments for IMZT and IMZO have been compared with those in structurally similar molecules and the need to obtain more reliable band assignments for some of the molecules considered is emphasised.     

Vibrational analysis and molecular structure of bipyrazine

A complete vibrational analysis of bipyrazine is presented, based on IR and Raman data and on the predictions of a valence force field initially transferred from 2,2′-bypirimidine. A set of refined force constants, obtained from the experimental data of both molecules, is also proposed to improve the agreement with observed data for the out-of-plane modes. Both experimental data and calculation suggest a centro-symmetric, trans planar conformation for bipyrazine. The vibrational assignment is discussed in terms of the kinetic energy distribution which, unlike the procedure based on the potential energy, is not influenced by numerical values of frequencies and force constants and allows unambiguous identification of normal modes in which each ring moves as a whole. Different frequency shifts for ring vibrations are predicted, for a model related to bipyrazine adsorbed to a metallic substrate through a nitrogen atom, in ortho or meta position relative to the inter-ring bond.     

Vibrational spectra and molecular conformations of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes

The Raman and IR spectra of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes have been measured. The normal coordinates have been calculated for these molecules using a consistent set of force constants and the molecular conformations studied by analysing the spectra with reference to the results of the calculations. In the crystalline solid state, 1,5-dichloropentane assumes the trans-trans-trans-gauche form and 1,5-dibromopentane, 1,6-dichloro- and 1,6-dibromohexanes assume the all-trans form. The normal coordinate treatment with the well-established force field was of great help in determining the whole molecular form of the relatively large chain molecules.     

Growth, spectral, and thermal characterization of 2-hydroxy-3-methoxybenzaldehyde semicarbazone

2-Hydroxy-3-methoxybenzaldehyde semicarbazone (HMBS) has been synthesized from 2-hydroxy-3-methoxybenzaldehyde and semicarbazide hydrochloride using sodium acetate as catalyst. Good quality single crystals of HMBS were successfully grown by slow evaporation method at room temperature using a mixture of DMF and ethanol as solvent. Fourier transform infrared and Fourier transform Raman spectral studies have been performed to identify the functional groups. Single-crystal XRD study was conducted to obtain the crystal structure and lattice parameters. The grown crystal was subjected to ¹H- and ¹³C-NMR spectral studies in order to confirm its structure and purity. The compound crystallizes into a monoclinic P21/c space group. Intermolecular hydrogen-bonding interactions facilitate unit cell packing in the crystal lattice. The UV–Vis spectrum confirmed the transparency of the compound between the wavelengths 420 and 1,100 nm, which is a characteristic property of a nonlinear optical (NLO) material. The thermal decomposition of the compound under static air atmosphere was investigated by simultaneous TG–DTG at a heating rate of 10 °C min^?1. The NLO property of HMBS was confirmed from the second-harmonic generation by Kurtz–Perry powder test.     

Vibrational analysis of 1,4-diiodobutane

Infrared and Raman spectra were obtained for 1,4-diiodobutane, and normal-coordinate calculations were made using a transferred 48-parameter modified v force field. This compound sometimes crystallizes in the GG' conformation with C₂ symmetry and sometimes in the TG conformation. No evidence was obtained for the presence of the TT (C_2h symmetry) or GG (C_i) conformers, but one or two additional conformers are present that must have a nonplanar chain of carbon atoms.     

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 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.