Spectrochimica Acta最新文献

It is shown that a complete parametrisation of the intensities of the CH-stretching vibrations of benzene and its derivatives is possible. The intensity I_CH for such a compound can be expressed by a relation I_CH=

Raman and infra-red spectra are reported for hexachlorocyclopropane (I), hexa-bromocyclopropane (II), hexafluorocyclopropane (III), tetrachlorocyclopropene (IV) and tetra-bromocyclopropene (V). A vibrational assignment is made for I, II and III on the basis of D_3h symmetry and for IV and V on the basis Of C_2v symmetry.

The absorption intensities of the CH and CD stretching vibrations of some deuterated benzene monoderivatives have been measured in CCl₄ solution. The compounds are of the type 4-D-phenyl-X and 2,4,6-D₃-phenyl-X. The observed intensities can be interpreted as sum of contributions I_o, I_m, and I_p, of the participating CH or CD oscillators. By using also the data for the undeuterated compounds phenyl-X these bond contributions can be evaluated separately. They show a decrease with the Taft substituent parameter σ_I, that is greatest in ortho and smallest in para position. The isotope intensity sum rule is verified for the CH and CD stretching vibrations in all the cases considered.

The analysis of infrared band shapes through correlation functions as developed by Gordon and Shimizu has been applied to the chloroethylenes. Reasonable agreement with Shimizu's theory has been achieved and the results compared with those of Gordon.

To analyse the interaction between substituents and aromatic CH bonds the intensities of the CH_ar stretching vibrations of 32 para-disubstituted benzene derivatives have been measured. For three discernible groups of p-benzene derivatives resulted a correlation between intensities and the sum of inductive parameters of Hammett constants [σ_I(X) + σ_I(Y)]. It was possible to invert the polarity of the moments of the CH bonds by strong electron acceptors. Hence the assumption of a C⁺H⁻ polarity in undisturbed benzene could be confirmed.

The infra-red spectra of synthetic hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, and mineral fluorapatite, Ca₁₀(PO₄)₆F₂, over the range 4000-250 cm⁻¹ are reported. Comparison with the “free” phosphate ion indicates considerable perturbation of the PO₄³⁻ group in these solids; the observed absorptions suggest that in both compounds the phosphate symmetry is lowered to the extent predicted by a site symmetry analysis i.e. to C₁ in hydroxyapatite and C_s in fluorapatite, but the splitting of degenerate modes is not complete; this effect is more noticeable in fluorapatite. A weak interatomic crystal field arising out of the relatively low density of the atomic packing in these compounds is suggested as a cause of this incomplete removal of degeneracies. The spectroscopic evidence for the existence of hydrogen bonding of the OH … OPO₃ type in hydroxyapatite is discussed.

Absolute infrared absorption intensities have been measured for three bands of crystalline acetylene and two bands (the hydrogen stretching motions) of crystalline ethane. The changes of intensity observed on condensation of the gases cannot be explained as a “dielectric effect”. In acetylene the large frequency shift and intensification of the hydrogen stretching mode are consistent with characterization of the intermolecular forces as hydrogen bonding to the acetylenic π-clouds.

The infrared spectra of dl-leucine and some metal-leucine complexes have been investigated from 3600 to 33 cm⁻¹. A detailed normal coordinate analysis was performed for the metal complexes and an approximate description of the vibrational mode has been assigned to most of the observed frequencies. Calculated values of the metal-nitrogen bond-stretching force constants vary in the order Pt(II) > Pd(II) > Cu(II) > Zn(II) > Cd(II) > Ni(II) ∼ Co(II) which indicates a corresponding variation in the strength of the metal-nitrogen bond.

The infra-red absorption spectra of liquid p-fluoro- and p-chloroanisole have been recorded. Vibrational assignments have been made on the basis of C_s symmetry.