Infrared spectra and normal coordinate analysis of bis(ethylenediamine) and bis(trimethylenediamine) complexes with copper(II)

The i.r. spectra of bis(ethylenediamine) and bis(trimethylenediamine) complexes of Cu(II) have been measured in the wave number region of 4000-250 cm⁻¹. Vibrational assignments have been made regarding the individual rings in both complexes. A normal coordinate analysis was performed using a modified general valence force field in order to check the empirical assignments. The agreement between the observed and calculated frequencies is satisfactory in view of the approximation used. A set of reliable force constants concerning most of the in-plane normal modes is obtained for the first time.     

SKELETON VIBRATIONS AND FORCE FIELD OF TWO ISOMOR-PHIC TRINUCLEAR μ_3-OXOFORMATO COMPLEXES OF IRON AND CHROMIUM

<正> The IR and Raman spectra for two isomorphic trinuclear μ3-oxo-formato complexes of iron and chromium were measured in the range 2000-110 cm-1.The assignments on the vibrations of the bridging and terminal coordinated formic ligands were made from the results of substitution reaction of the latter.A simplified model and a simplified general valence force field were used in normal coordinate analysis.The calculated frequencies agree well with the observed values,with a mean deviation of 1.1% for [Fe3O17C] and 0.9% for [Cr3O17C],confirming our assignments of their vibrational spectra.Two sets of the force constants have been calculated.In terms of the relationship among the vibrational frequencies,structure and some properties of the compounds,the rationality and reliability of the results were discussed.     

Spectroscopic studies of Lewis acid-base complexes: Part V. Raman and infrared spectra,assignments and normal coordinate analysis for difluorophosphine borane

Raman spectra of five isotopic species of HPF₂BH₃ have been obtained in the liquid and solid states together with infrared spectra of the same species in the gaseous and solid states. Vibrational assignments have been made with the aid of a normal coordinate analysis utilizing compliance constants. Both compliance and force constants are reported. The force field is quite similar to that of PF₃BH₃ despite the marked difference in stability of the two compounds.     

In-plane vibrational modes of cytosine from an ab initio MO calculation

Harmonic force constants, in-plane vibrational frequencies, and in-plane vibrational modes of cytosine were calculated by an ab initio Hartree—Fock SCF MO method. The force contants were calculated by the use of an energy gardient method with the STO-3G basis set, and then they were corrected into “4-31G force constants” by the scaling factors given by us previously for the case of uracil. The corrected set of force constants can produce a calculated vibrational spectra of cytosine and cytosine-1,amino-d₃, that can be well corrected with the observed Raman and infrared spectra of these compounds, with little ambiguity. Thus, the assignments of all the in-plane vibrations are now practically established. The calculated vibrational modes, in addition, can account for the recently published resonance Raman effects of cytosine residue.     

Theoretical prediction of vibrational spectra: the harmonic force field and the vibrational spectrum of 4-methylpyridine

The geometry, complete harmonic force field and dipole moment derivatives have been computed for 4-methylpyridine at the Hartree-Fock level using a 4-21 basis set of Gaussian orbitals. A set of eleven scale factors, six of which were previously derived from benzene and the other five for the vibrational motions of the methyl group from toluene by fitting their computed force fields to their observed vibrational spectra, was used to scale the computed harmonic force constants of 4-methylpyridine. The vibrational frequencies and the associated infrared absorption intensities of 4-methyl -pyridine were then predicted from this scaled force field without any fitting to the experimental data of 4-methylpyridine. Comparison with experimental spectra permitted a few corrections to be made in previous experimental or semiempirical assignments. The mean-deviations between experimental and predicted frequencies was only 5.6 cm^-1 for the non-CH stretching frequencies or 8.3 cm^-1 overall. Computed intensities are qualitatively m agreement with experiment. The optimization of scale factors for the five methyl vibrational motions produced a trivial improvement in the fit.     

Ab-initio molecular geometry and normal coordinate analysis of pyrrolidine molecule.

The molecular geometry of pyrrolidine was quantum mechanically calculated using the split valence 6-31G** basis set. Electron correlation energy has been computed employing MP2 method. The molecule showed an envelope form puckered structure with inter-plane angle of 36.4 degrees and has a total energy of -132976.80 kcal mol(-1) of which a -464.86 kcal mol(-1) electron correlation energy. The twist form of the molecule showed a twist angle of 10.2 degrees from planarity and has a total energy of -132976.05 kcal mol(-1) involving -464.097 kcal mol(-1) electron correlation energy. The normal coordinates of the molecule were theoretically analyzed on the basis of the Cs point symmetry of the envelope form. Using initial set of force constants obtained from the ab-initio calculations the fundamental vibrational frequencies were computed. The IR and laser Raman spectra of Pyrrolidine molecules were measured. All the observed vibrational bands including combination bands and overtones were assigned to normal modes with the aid of the potential energy distribution values obtained from normal coordinate calculations. The molecular force field was obtained by refining the initial set of force constants using the least square fit method. The molecular force field was determined by refining the initial set of force constants using the least square fit method instead of using the less accurate scaling factor methods. The determined molecular force field has produced simulated frequencies best match to the observed values. The low frequency molecular out-of-plane deformation modes were observed in both infrared and Raman spectra at 298 and 163 cm(-1). The barrier of ring twisting estimated from the observed ring out-of-plane vibrational mode at 163 cm(-1) was found 3.1 kcal mol(-1).     

Theoretical prediction of vibrational spectra. The a priori scaled quantum mechanical (SQM) force field and vibrational spectra of pyrimidine

The complete harmonic force field of pyrimidine has been computed at the ab initio Hartree—Fock level using a 4–21 Gaussian basis set. In order to compensate the systematic overestimations of the force constants at the aforementioned level of quantum mechanical approximation, the theoretical force constants were empirically scaled by using nine scale factors. (The values of all these scale factors were previously determined by fitting the theoretical force field of benzene to the observed vibrational spectra of benzene.) The resulting a priori scaled quantum mechanical (SQM) force field is regarded as the most accurate and physically the most correct harmonic force field for pyrimidine. This force field was then used to predict the vibrational spectra of pyrimidine-h₄ and pyrimidine-d₄. On the basis of these a priori vibrational spectra uncertain assignments have been confidently resolved. After a few reassignments, the mean deviations between the experimental and calculated frequencies are below 9 and 18 cm⁻¹ for the non-CH stretching in-plane and the out-of-plane vibrations, respectively. Computed IR intensities are generally in agreement with experiments at a qualitative level.     

[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的红外光谱和简正坐标分析

在500—100cm~(-1)波段范围内测定了[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的Fourier变换红外光谱。采用简化的普遍价力场(SGVFF)进行了简正坐标分析,振动基频的计算值与观测值符合良好,两者平均偏差小于1.0％,证实了振动谱带的归属,确定了相应的力常数。最后讨论了谱带归属问题和所得结果的合理性和可靠性。     

Normal coordinate and infrared band intensities of trichloronitromethane and trichloroacetate ions

Laser Raman and IR spectra in the region 50–3000 cm⁻¹ for trichloronitromethane and trichloroacetate ions were recorded. All observed vibrational bands have been assigned to normal modes. Normal coordinate analyses of these molecules have been carried out in the valence force-field approximation. A set of force constants was obtained leading to good agreement between observed and calculated frequencies. The relative displacements of the atoms resulting from normal coordinate calculations were used to compute the IR band intensity of each mode by the CNDO/2-MO procedure. The intensity calculations confirmed the assignments and supported the calculated force constants.     

Vibrational spectra and normal coordinate analysis of diazepam, phenytoin and phenobarbitone

Vibrational spectroscopy is an important tool for the structural investigation of the organic molecules. In the present investigation, a normal coordinate analysis has been carried out on some anti-epileptic drugs, viz. diazepam, phenytoin and phenobarbitone. Diazepam is a derivative of benzodiazepine, phenytoin is a derivative of hydanation and pheonobarbitone is a barbiturate. The infrared spectra of the compounds are recorded in the region 4000-400 cm(-1) and Raman spectra are recorded in the region 3500-50 cm(-1). From the structural point of view, diazepam, phenytoin and phenobarbitone have been assumed to C(s) point group. A systematic set of symmetry coordinates has been constructed for these compounds and Wilson's FG matrix method has been applied for the normal coordinate analysis using general quadratic valance force field. The potential energy distribution is also calculated to check the vibrational band assignments.     

三羟甲基甲胺的红外和Raman光谱研究和简正坐标分析

在4000—50cm~(-1)波段范围内测定了三羟甲基甲胺晶体分子的红外光谱和Raman光谱。采用简化的普遍价力场(SGVFF)进行了简正坐标分析。振动基频的计算值与观测值符合良好。两者平均偏差小于1.0％,证实了振动谱带的归属,确定了相应的力常数。最后讨论了谱带的归属问题和所得结果的合理性和可靠性。     

Force constant calculations on methyl phosphorus(III) dicyanide and methyl arsenic(III) dicyanide,CH3P(CN)2 and CH3As(CN)2

The force constants of methyl phosphorus(III) dicyanide and methyl arsenic(III) dicyanide have been calculated using a simple valence force-field approximation with interaction constants. The assignments of the observed infrared and Raman spectra are discussed in the light of these calculations. Several revisions of the previous tentative assignments are proposed.     

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.     

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.     

Harmonic dynamics of beta-D-fructopyranose

The vibrational spectra of beta-D-fructopyranose crystals have been recorded in the 4000-400 cm(-1) region using the infrared and in the 4000-20 cm(-1) region using the Raman. These spectra are used as an experimental basis in order to establish a force field for the beta-D-fructopyranose molecule in the crystalline state through a normal co-ordinates analysis. For this purpose, a modified Urey-Bradley-Shimanoushi force field was combined with an intermolecular potential energy function that includes the van-der-Walls interactions, the electrostatic terms, and an explicit hydrogen bond function. The force field parameters are derived from those of beta-D-glucose and are fitted so as to obtain a good agreement between the calculated and the observed frequencies. The results obtained demonstrate the reliability and the transferability of the set of parameters constituting the initial force field. The fitted force field reproduces the experimental spectra to a marked degree of accuracy.     

Vibrational spectra of succinonitrile and its [1,4-13C2]-,[2,2,3,3,-2H4]- and 1,4-13C-2,2,3,3-2H4]-isotopomers and a force field of succinonitrile

[1,4-13C2]-succinonitrile, [2,2,3,3-2H4]-succinonitrile, [1,4-13C2-2,2,3,3-2H4]-succinonitrile have been synthesized and, for the first time, the infrared and Raman spectra of these succinonitrile isotopomers have been discussed in detail. The spectra were recorded at ambient temperature and at the temperature of liquid nitrogen and assignments of the vibrational bands of all above isotopomers have been made. In addition to this, the force field of succinonitrile in its two configurations, gauche and trans, have been calculated using all experimental frequencies and the ab-initio method. Also, the assignments of the vibrational bands of the 'normal' succinonitrile molecule have been achieved using the results of the force field calculations to support the assignments for the normal succinonitrile, as well as for the isotopomers.     

Vibrational spectra,scaled quantum-mechanical (SQM) force field and assignments for 4H-pyran-4-one

The gas phase i.r. spectrum of 4H-pyran-4-one (hereafter called γ-pyrone) has been recorded in the 4000-400 cm⁻¹ region by a Nicolet 7199 FTIR spectrometer and interpreted using a general valence force field calculated quantum mechanically at the ab initio level with a split-valence 4–21 basis. Assignment of certain fundamentals was facilitated by information gained from the i.r. and Raman spectra of the melt and from the i.r. spectrum of the saturated solution in CCl₄.To account for systematic computational errors, the theoretical ab initio force field was scaled using a set of constants derived by the empirical fitting of force fields computed for related molecules to their observed spectra. Either the scale factors derived for a family of open-chain molecules or, better, for benzene could be used to yield a scaled force field which gave unequivocal assignments for γ-pyrone. The method promises to be of general applicability for molecules of this complexity.     

Normal coordinates analyses of disaccharides constituted by D-glucose, D-galactose and D-fructose units

A thorough study of the vibrational spectra of two disaccharides, melibiose and turanose, is presented in this work. The infrared and Raman spectra of these two compounds have been first recorded in the mid infrared range then in the far infrared region (for Raman only). These spectra constitute the main experimental support for the calculations of the modified Urey-Bradley-Shimanouchi force fields of these two disaccharides. Good agreements have been obtained between the observed and calculated frequencies. In a second time, spectra of O-deuterated derivatives have been recorded and used in order to confirm some of the frequency assignments and to test the validity of the obtained force fields.     

The computed force constants and vibrational spectra of toluene

The complete harmonic force field and dipole moment derivatives have been computed for toluene at the Hartree-Fock level using a 4-21G basis set. The six scale factors optimized for benzene were used to scale the computed harmonic force constants of toluene. The vibrational frequencies of toluene computed from this scaled quantum mechanical force field are quite good. After a correction was made to two previously proposed spectral assignments, the mean deviation from the experimental frequencies is only 7.8 cm^?1 except for the frequencies related to the methyl group. Five more scale factors for the vibrational modes of the methyl group were reoptimized. The final comparison showed an overall mean deviation of 7.5 cm^?1 between the theoretical spectrum and the experimental spectrum. Computed intensities are qualitatively in agreement with experiments. They are highly useful in the investigation of questionable assignments.