Spectrochimica Acta最新文献

It is shown that the derivation of equations of Polo and Wilson and of Mallard and Straley for solvent effects in vibrational spectroscopy does not take into account the change of molecular polarizability during vibrations. This change can be accounted for by considering the effective dipole moment and polarizability of solute molecule, as given by Onsager's theory of dielectric polarization, and their derivatives with respect to the normal coordinate. In this way new equations are derived for solvent effects on infra-red and Raman intensities.

Thermodynamic ionization constants over the temperature range 10–60° together with values for the standard free energy, enthalpy and entropy of ionization of m-chlorophenol, m-bromophenol and m-iodophenol are reported. These results in conjunction with an extensive collection of similar results from the literature show that substituent effects in the ionization of phenols are due primarily to entropy changes possibly involving a change of solvation state. In contrast to the free energies of ionization the entropies are well correlated by σⁿ values.

The nuclear magnetic resonance spectra of aqueous solutions of three β-hydroxy carboxylic acids and some of their derivatives were measured as a function of the pH. The chemical shifts of the methylene hydrogens, adjacent to the carboxyl group, exhibit titration curves. The chemical shift between the two methylene hydrogens behaves differently in each compound, the most common behaviour being the occurrence of a minimum in the shift at pH ⋍ pK. The value of the spin—spin coupling constant changes only very slightly with the pH. The effect of added neutral salts and the variation of the temperature were also investigated in some of the acids. Qualitative conclusions concerning inter- and intramolecular hydrogen bonds and electrostatic interactions in these molecules were derived from the results.

Since the spectrum of the resonance radiation from an atomic vapour consists only of those spectral lines which are absorbed by the vapour, resonance lamps can serve as monochromators for isolating those lines whose intensities are measured in atomic absorption spectrophotometry. Resonance lamps in which the atomic vapour is produced by indirect electrical heating of the appropriate metal in a rare gas at reduced pressure are suitable as monochromators for use in the determination by atomic absorption measurement of low-melting-point metals such as calcium, magnesium, sodium, potassium, thallium and lead. Similar techniques offer attractive possibilities for the construction of simple calorimeters for specific determinations.

Far infra-red spectra of the hexanitrocobalt (III) complex salts, M₃[Co(No₂)₆] (M: Na, K, Rb and Cs), and the hexammine complex salts, [Co(NH₃)₆]X₃ (X: Cl, Br and I) and [Ni(NH₃)₆]Cl₂, have been measured down to 25 cm⁻¹. In addition to the intramolecular vibrations in the complex ion (the metal—ligand stretching and deformation vibrations associated with the co-ordination bond), the lattice vibrations due to the interaction between the complex ion and the outer ion have been observed in the region below 150 cm⁻¹.

A normal co-ordinate analysis of the crystal as a whole has been performed and the interaction potential constants as well as the intramolecular potential constants have been obtained by using the observed frequencies for both of the lattice vibrations and the intramolecular vibrations. It has been found that the lattice frequencies may be explained by taking into consideration the interaction between the atoms or ions whose interatomic distances are shorter than 3·5 Å. It has been shown that some of the intramolecular potential constants should be somewhat modified by the introduction of the lattice vibrations, but the metal—ligand stretching force constant may be almost accurately obtained without considering the lattice modes.

Far infra-red spectra of the halogenoammine cobalt (III) complex salts have been also measured and several bands attributed to the lattice vibrations have been obtained.

The ν_OH bands of a series of ferrocenyl alcohols and phenols have been studied as a function of temperature in carbon tetrachloride. From this, enthalpies have been calculated for the interaction of the hydroxyl group with both the ferrocenyl π-electrons and the d-orbitals of iron. The accessibility of the iron d-orbitals has been compared with those of the d-orbitals in the corresponding ruthenium and osmium compounds.

The shifts of the infra-red frequencies of [1.4—¹³C₂]-cyclohexane-(1.4)dione and [1.4—¹³C₂]-p-benzoquinone in the solid state, in solution, and in the vapour phase are discussed in relation to band assignments given in the literature.

Infrared intensity measurements of cis and trans isomers of 4-t-butylcyclohexyl chloride in CS₂ solution show that the apparent molecular extinction coefficient for the equatorial CCl stretching vibration is 60 percent greater than the value for the axial CCl stretching vibration. The integrated absorption intensity is 47 percent greater for the trans isomer. Dilute solutions of the individual isomers conformed to Beer's Law. No solute—solute interaction was observed for solutions of isomeric mixtures.