Fourier transform infrared spectra of three titanium tetrachloride-ethyl benzoate complexes. Assignment based on five isotopic homologues and extension of the ethyl benzoate force field

FTIR spectra (200–1750 cm⁻¹) are given for (TiCl₄EB)₂, (TiCl₄)₂EB and TiCl₄EB₂, where EB is ethyl benzoate. A full assignment is given for (TiCl₄EB)₂ based on extension of an ethyl benzoate force field and four isotopically labelled complexes with ¹⁸Ocarbonyl-EB, d₅-EB, Ed₅-B and d₅-Ed₅-B. There is no evidence for bidentate complexation or complexation through the ether oxygen in any of the complexes. A strong coupling between the αCO stretching vibration and the ethyl group deformations can make simplified interpretations of differences between spectra misleading.     

Vibrational analysis and FTIR spectra of seven isotopic congeners of ethyl benzoate including18O carbonyl and ether labelled esters

FTIR spectra of seven isotopic congeners of ethyl benzoate are fitted to a force field with a standard deviation of less than 7 cm^–1. The field has been transferred to ethyl anisate and an equimolar titanium tetrachloride-ethyl benzoate complex with encouraging success. The band at 1280cm^–1 is definitely assigned as mainly an-C-O stretch.     

F.t.i.r. and Raman spectra of triphenylphosphine,triphenylarsine, triphenylstibine,and dibenzylsulphide

The f.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide in the solid state at ca 80 K have been recorded over the ranges 3500-40 cm⁻¹ (infra-red, 1 cm⁻¹ resolution) and 1650-30 cm⁻¹ (Raman, 2 cm⁻¹ resolution). The data, particularly those in the low wavenumber region, are more extensive, more complete, and of higher quality than those obtained in previous studies. Detailed band assignments are given.     

Theoretical prediction of vibrational spectra. Scaled quantum mechanical (SQM) force field for fluorobenzene

The complete harmonic force field of fluorobenzene has been determined from ab initio Hartree-Fock calculations using the 4–21 Gaussian basis set. As force constants are systematically overestimated at this level of theory, the directly calculated force field was scaled by empirical factors taken over from benzene and methylfluoride. Except for a slight overestimation of the CF stretching frequency, the scaled quantum mechanical (SQM) force field obtained in this way reproduces the experimental fundamental frequencies of the parent molecule and two deuterated isotopomers within 20 cm⁻¹ (with mean deviations below 12 cm⁻¹), and experimental assignments are analyzed on this basis. Theoretical i.r. intensities reproduce the main features of the spectra fairly well.     

Infrared and Raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of ethyl methyl selenide

The Raman spectra (3200–10 cm⁻¹) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200–30 cm⁻¹) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158±16 cm⁻¹ (452±46 cal mol⁻¹), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the STO-3G* and 4–31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules.     

Vibrational analysis of 2-nitrophenol. A joint FT-IR,FT-Raman and scaled quantum mechanical study

FT-IR (gas, solution, solid) and FT-Raman (solution, solid) spectra of 2-nitrophenol have been recorded in the range of 4000–30 cm⁻¹. The spectra were interpreted with the aid of normal coordinate analysis based on a scaled Becke3–Lee–Yang–Parr/6-31G^* density functional force field utilising a set of scale factors introduced recently by Rauhut and Pulay (G. Rauhut, P. Pulay, J. Phys. Chem. 99 (1995) 3093). These scale factors, developed on a small training set of organic molecules containing no hydrogen bonding moieties, were found to be well transferable to 2-nitrophenol including the strong intramolecular (O)H⋯O(N) hydrogen bonding moiety as well. The scaled force field reproduced the experimental frequencies of the molecule by a weighted mean deviation of 10.5 cm⁻¹. Based on the calculated results, 38 fundamentals from a total of 39 were identified and assigned, revising the assignments of earlier experimental studies for several fundamentals.     

FT-Raman and infrared spectra,r0 structural parameters,ab initio calculations and vibrational assignment for nitryl chloride

The FT-Raman spectra (2000-30 cm⁻¹) of liquid and solid nitryl chloride, ClNO₂, along with the infrared spectra (2000-80 cm⁻¹) of the gas and solid have been recorded. All six fundamentals are confidently identified and the potential energy distributions determined from the force fields obtained from ab initio calculations. Several different basis sets have been utilized to determine the harmonic frequencies and force constants which are compared to the previously reported valence force constants. Structural parameters have been calculated with these basis sets including electron correlation with MP2, MP3 and MP4 perturbation. The calculated equilibrium structural parameters are compared to the experimental r₀ structural parameters. The spectra of the solid indicate that there are at least two molecules per primitive cell. All of these results are compared to the corresponding quantities for some similar molecules.     

Vibrational spectra and valence force field calculation of deltic acid

Infrared and Raman spectra of crystalline deltic acid and its deuterated derivative have been studied between 4000 and 20 cm⁻¹. In order to specify vibrational assignment of ring and CO modes based on C_2v molecular symmetry, valence force field calculation was undertaken. It appears that the results obtained for simpler disubstituted cyclopropenones can be applied to deltic acid. So, the highest frequencies about 1930 and 1610 cm⁻¹ involve nearly equal mixture of ring and CO stretching. Two different, strong but asymmetric OH

OC hydrogen bonds occur in crystal.     

Infrared and Raman spectra of terephthalonitrile and terephthalonitrile-15N2. Force field for out-of-plane vibrations

A general assignment of the vibrational spectra of terephthalonitrile and terephthalonitrile-¹⁵N₂ is proposed on the basis of their infrared and Raman spectra. The relevant symmetry is found to be D_2h. The force field for the out-of-plane vibrations of these molecules was calculated by refining the general quadratic force field obtained by the semi-empirical MINDO/3 method, starting with a geometry optimized by this method. The refined force field reproduces the observed frequencies of the out-of-plane vibrations to better than ±0.5 cm⁻¹.     

Vibrational analysis of trans,Trans,trans-2,3,4,5-tetrachlorohexa-1,3,5-trienes

Infrared and Raman spectra of t,T,t-2,3,4,5-tetrachlorohexa-1,3,5-triene were measured in liquid and crystalline phases. It is suggested that the non-planar structure of this compound may be due to the 1–3 effect. In the liquid state a mixture of rotational isomers, of C₂ and C_i symmetry, was confirmed by the freezing-out of some characteristic bands in the 1600 cm⁻¹ region in the IR and Raman spectra of the t,T,t-compound. Normal coordinate analysis was carried out using force constant values from the force field previously determined for chloroderivatives of buta-1,3-diene. A complete assignment of observed frequencies is proposed.     

Infrared and Raman spectra,vibrational assignment and normal coordinate calculations for ethylisothiocyanate-d0 and -d5

The i.r. spectra (3500-40 cm⁻¹) of gaseous and solid ethylisothiocyanate, CH₃CH₂NCS, and ethylisothiocyanate-d₅, CD₃CD₂NCS, and the Raman spectra (3200-10 cm⁻¹) of the liquids and solids have been recorded. Additionally, the i.r. spectrum of matrix (N₂) isolated CH₃CH₂NCS was recorded from 3500 to 200 cm⁻¹. The vibrational spectra have been interpreted on the basis of a cis form of C_s symmetry for all three physical states; however, in the spectum of the matrix isolated sample at 10 K, several of the fundamentals are doublets which may be arising from two conformers at this temperature. A vibrational assignment is given based on i.r. band contours, depolarization values, isotopic shifts and group frequencies. The assignment is supported by the Teller—Redlich product ratios. The methyl torsion was observed at 270 cm⁻¹ in the solid phase which gives a periodic barrier of 4.7 kcal/mole. A normal coordinate calculation has been carried out utilizing a modified valence force field consisting of 15 diagonal force constants and seven interaction terms which reproduced the observed frequencies with an error of 1.45% for the -d₀ molecule and 3.40% for the -d₅ compound. Because of the large CNC angle (∼ 145°) and low barrier to internal rotation of the asymmetric rotor, the skeletal bend and torsion couple to give a very broad band with two maxima and apparent P band heads. These results are compared to corresponding studies of similar molecules.     

Structure,vibrational assignment,normal coordinate analysis,and ab initio calculations of methylisocyanate

The infrared (3200-30 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra of gaseous and solid methylisocyanate, CH3NCO, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios have been measured. The CNC bend has been observed in the far infrared and low frequency Raman spectra of the gas at approximately 172 cm⁻¹. An additional far infrared band at ≈50 cm⁻¹ has tentatively been assigned as the methyl torsional mode, although it could be due to the Δν = 1, Δl = ± 1 transitions of the CNC bending mode. A complete assignment of the vibrational fundamentals is proposed. The structural parameters, force constants, and vibrational frequencies have been determined from ab initio Hartree—Fock gradient calculations using the 6-31G* basis set. Additionally, structural parameters have been obtained with the 6-311 + + G** basis set with electron correlation at the MP2 level which are compared to those obtained from the microwave data and electron diffraction study. These results are compared with the corresponding quantities obtained for similar molecules.     

Molecular mechanics investigation of some acrylic polymers using SPASIBA force field

The First generation SPASIBA force field is used to study normal vibrational modes of PMMA, and then extended to other thermoplastic polymers, namely PMA, PMAA and PAA, in order to determine its parameters transferability. To this end, FTIR and FTR spectra of pure PMMA samples, prepared by the emulsion polymerization of MMA and initiated by sodium, are recorded in 400–3500 cm⁻¹ and 200–3500 cm⁻¹, respectively. A detailed vibrational analysis was performed on the obtained spectra and the observed frequencies are assigned to their respective vibrational modes, supported by potential energy distribution (PED) analysis. Our numerical results reveal an RMS value of 7.8 cm⁻¹ corresponding to IR wavenumbers and 8.7 cm⁻¹ relatively to Raman wavenumbers. Our vibrational calculations on PMA, PMAA and PAA polymers reveal that the parameters transferability criterion, established by Shimanouchi, is verified for the SPASIBA force field.     

A vibrational molecular force field of model compounds with biological interest—III. Harmonic dynamics of α- and β-d-galactose in the crystalline state

The infrared spectra of α- and β-d-galactose were recorded, both in the mid-IR range (4000-500 cm⁻¹) and in the far-IR (500-50 cm⁻¹). The Raman spectra were also obtained. These spectra constitute the basis of a crystalline-state force field established for these two molecules through a normal coordinate analysis. A modified Urey—Bradley—Shimanouchi force field was combined with an intermolecular potential energy function which includes van der Waals interactions, electrostatic terms and an explicit hydrogen bond function. The force constants were varied, so as to obtain an agreement between the observed vibrational frequencies and the calculated ones of α-d-galactose. The force field obtained was then applied to α-d-galactose O-d5 and β-d-galactose, in order to test its transferability. The computed potential energy distribution was found to be compatible with previous assignments for d-glucose, particularly for the modes involving C6 and COH groups. For β-d-galactose the same force field was used with changing the force constants due to the C1 and C6 groups.     

Spectra and structure of silicon compounds. XVII Raman and infrared spectra and vibrational assignment for hexamethyldisilane and ab initio calculations for disilane and hexamethyldisilane

The IR spectra of gaseous and solid hexamethyldisilane between 4000 and 25 cm⁻¹ and the far-IR spectrum of the liquids from 450 to 25 cm⁻¹ have been recorded. The Raman spectra have been recorded from 3500 to 10 cm⁻¹ for all three physical phases. Assisted by ab initio calculations, the vibrational spectrum of hexamethyldisilane has been assigned under D_3d symmetry and the results of a normal coordinate analysis are discussed. No spectral features indicative of free internal rotation have been observed. Gradient ab initio calculations have been carried out for the disilane and hexamethyldisilane molecules using different types of basis sets. The structural parameters, rotational constants, unscaled and scaled frequencies and harmonic force constants have been reported for both disilane and hexamethyldisilane.     

Theoretical study on the structures,force field,and vibrational spectra of cyclooctatetraene and cyclooctatetraene-d8

The structures and force field of 1,3,5,7-cyclooctatetraene (COT) have been studied using ab initio theory at the SCF level with the 4-21G basis set. The quadratic force field of the D_2d structure obtained by systematic scaling of the ab initio force constants successfully reproduces the observed frequencies of COT and COT-d₈ with a mean deviation of less than 10 cm⁻¹ for non-CH stretching modes. On the basis of the calculated results, assignments of the fundamental vibrations are examined. The normal mode υ₅ is reassigned to a weak band at 758 cm⁻¹ in the Raman spectrum of COT and to a weak band at 591 cm⁻¹ in the Raman spectrum of COT-d₈. The calculations favor the assignment of υ₂₆ given by Lippincott et al. [J. Am. Chem. Soc. 73, 3370 (1951)] over the revised assignment of Perec [Spectrochim. Acta 47A, 799 (1991)]. The calculations also furnish reliable prediction for the inactive A₂ fundamentals of COT and COT-d₈. The fundamental frequencies and IR and Raman intensities of ¹³CC₇H₈, which constitutes about 9% of COT in natural abundance, are also calculated. Only ν₁₀ (calculated at 908 cm⁻¹) of the formal inactive A₂ modes has appreciable Raman intensity (0.23 Å⁴/amu). A spectral feature due to this fundametal is identified in the liquid Raman spectrum of Tabacik and Blaise [C. R. Acad. Sci. Ser. II 303, 539 (1986)] as a weak peak at 908 cm⁻¹.     

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 normal coordinate calculations for dimethyltelluride-d0, -d6 and dimethyltellurium difluoride-d0, -d6

The i.r. (4000-30 cm⁻¹) and Raman (4000-O cm⁻¹) spectra of dimethyltelluride, dimethyltellurium difluoride and their deuterated analogs have been obtained. All the active fundamentals of these compounds except methyl torsions were assigned, assuming a C_2υ molecular symmetry for both the tellurides. Normal coordinate calculations have been made in order to confirm the proposed assignments. The skeletal bond strength of the tellurides together with that of TeF₄ are discussed, using the valence stretching force constants.     

The Raman and IR spectra and normal coordinate analysis of 3-(N-phenylacetylamino)-2,6-piperidinedione,Antineoplaston A10, the new antitumour drug

The Raman and IR spectra of 3-(N-phenylacetylamino)-2,6-piperidinedione, Antineoplaston A10, the new antitumour drug and its N,N-dideuterated derivative have been recorded in the range 4000-30 cm⁻¹. Vibrational assignments are given and are supported by normal coordinate calculations based on a general valence force field. The interaction force constants were transferred intact from the scaled ab initio force fields of structurally related molecules. The calculated frequencies are in very good agreement with the experiment. A striking similarity is noted for frequencies of the corresponding vibrations in Antineoplaston A10 and in uracil derivatives. The results obtained support previous theoretical predictions that the mechanism of action of A10 may be related to its structural and electronic resemblance with pyrimidine bases. The drug may act as their antagonist in the electrostatic interaction and hydrogen bonding formation with biological molecules.     

Crystalline sulfur dioxide: Crystal field splittings,absolute band intensities,and complex refractive indices derived from infra-red spectra

The infra-red absorption spectra of thin crystalline films of sulfur dioxide at 90 K are reported in the 2700-450 cm⁻¹ region. The observed multiplicity of the bands in the regions of fundamental modes is attributed to crystal field effects, including factor group and LO—TO splittings, and naturally present minor ³⁴S, ³⁶S and ¹⁸O substituted isotopic species. Complex refractive indices determined by an iterative Kramers—Kronig analysis of the extinction data, and absolute band strengths derived from them, are also reported in this region.