Spectrochimica Acta最新文献

The validity of various sets of assigned in-plane vibrational frequencies for boron trihalides is discussed by application of the product rule, and by comparison of the signs of symmetry force constants calculated from the observed frequencies with those predicted by using of the hybrid orbital force field. The Urey—Bradley force constants were modified and translated from the general valence force constants so as to be compatible with the information obtained above, and consistent with the empirical data for a series of molecules of this structural type. As a result, it was found that the bond—bond, angle—angle and bond—opposite angle interaction should necessarily be taken into consideration for obtaining the reasonable modification.

Evidence for the formation of complexes between fumaronitrile and iodine monochloride is given by NMR, infra-red and visible absorption spectra.

The ultra-violet spectra of thiazoline-2-thione, thiazolidine-2-thione, benzthiazoline-2-thione, 3(N)-methyl-benzthiazoline-2-thione and 2-methyl-thiobenzthiazole in a range of solvents have been determined, solvent effects noted and assignments given for the main absorption bands. The spectra of thiazoline-2-thione and thiazolidine-2-thione are interpreted by their relationship to the spectra of dithiocarbamates, the intense long-wavelength ultra-violet absorption band in the spectra being assigned to an intramolecular charge-transfer transition involving the thioamide grouping. The ultra-violet spectra of benzthiazoline-2-thione and 3(N)-methyl-benzthiazoline-2-thione are related to the spectra of benzthiazole and thioamides. The very intense long-wavelength band in the spectra of these compounds is also assigned to an intra-molecular charge-transfer transition involving the thioamide grouping. The spectrum of 2-methyl-thiobenzthiazole is related to that of benzthiazole and also contains an intense long-wavelength band which is assigned to an intra-molecular charge-transfer transition involving the NCS grouping.

The spectrum of benzthiazoline-2-thione in twenty-five solvents is reported and the solvent dependence of the charge-transfer band noted. Blue shifts are observed in hydroxylic solvents where hydrogen bonding from solvent to the thione sulphur atom occurs and red shifts in solvents where the benzthiazoline-2-thione functions as a hydrogen bond donor. In solvents where the compound acts as both a donor and acceptor zero shifts are observed.

These conclusions are supported by the studies, in a range of critical solvents, of the spectrum of the N-methyl derivative which can function as a hydrogen bond acceptor only, and hence shows blue shifts only.

The infra-red spectra of sulphamide and sulphamide-d₄ have been recorded for ordinary and polarized radiations. The vibrational assignment has been made by referring to the infra-red dichroism as well as to the isotopic effect. Normal co-ordinate analysis of sulphamide and sulphamide-d₄ as nine atomic molecules has been carried out by assuming the molecular symmetry of C_2ν. The calculation of potential energy distributions has shown that the shift of the NSN symmetric and antisymmetric stretching bands on N-deuteration is attributed to the vibrational coupling between the SN stretching and the ND₂ bending vibrations.

The infra-red spectrum of ortho-phosphoric and deutero ortho-phosphoric acids have been measured in acetonitrile, dioxan, acetone and tetrahydrofuran. The frequencies associated with the symmetric PO and PO stretching vibrations are observed to move apart from their observed frequencies in aqueous solutions. The observed data is shown to be consistent with accepted values of force constants for PO and PO bonds. There is uncertainty in the frequency of the lowest e fundamental.

Fatty acids undergo self-association and form 1:1 molecular complexes with pyridine on mixing the ingredients in the low dielectric solvent carbon tetrachloride. Infra-red spectroscopic studies of the pyridine—fatty acid—carbon tetrachloride system confirm the existence of a tautomeric equilibrium involving the ion-paired and non-ion-paired associated complexes in the solution as is represented below:

The dimerization constants (K_D) for the dimerization equilibria of palmitic and myristic acids in carbon tetrachloride have been estimated by a new method as K_D = 1·34 ± 0·2 × 10³ mole⁻¹ l (palmitic acid) K_D = 1·28 ± 0·2 × 10³ mole⁻¹ l (myristic acid).

The present study has given the following values for the equilibrium constants of the above equilibria (1).

Palmitic acid Myristic acid K₁ = 4·6 ± 0·5 K₁ = 3·6 ± 0·5 K₂ = 2·6 ± 0·5 K₂ = 2·0 ± 0·5 K_T = 0·57 K_T = 0·56

The presence of two species of the complex can be explained in terms of a double potential energy curve for the hydrogen bond system.

The infra-red spectra of pyrimidine-d₀ and -d₄ have been measured between 4000 and 300 cm⁻¹ in gas, liquid and solid phases. Since the analysis of the rotational band envelopes alone was not sufficient for a definite assignment, useful information was gained from the interpretation of the crystal spectra in polarized light of both isotopic species.

A new vibrational assignment is presented which differs from that given previously by Lordet al. for the six fundamentals ν_6a, ν_19a, ν_6b, ν_18b, ν_19b, ν₄. The experimental evidence for the new assignment is discussed in detail.

The spectra of 63 compounds have been recorded as mulls in Nujol and in hexachlorobutadiene and as alkali halide discs. The effect of site symmetry on the gross structure of the spectra and on the intensity of ν₁ is considered; the effect of perturbation by water molecules, and the possibility of covalent bonding in the compounds is also discussed.

The preparation of 1,4-dioxadiene is described and the Raman spectrum of the liquid and infra-red spectra of the liquid and gas phases are reported. A vibrational assignment is proposed and it is concluded that the molecule is planar and is not highly conjugated.