Quasiline fluorescence and absorption spectra of NH-isomers of octamethylisobacteriochlorin

Quasiline fluoresence and fluorescence excitation spectra of NH-isomers of 2,2,7,7,12,13,17,18-octamethylisobacteriochlorin (cis- and trans-) in polycrystalline matrices in n-hexane and n-octane at 4.2 K are obtained. A vibration analysis of the spectra in combination with the data of quasiline spectra of cyano-substituted octaethylisobacteriochlorin and octamethylporphin permitted a qualitative interpretation of the vibronic spectra of NH-isomers. It is inferred that for a trans-isomer, the 0–0 transition S₂⇃S₀ is localized in the region of electron-vibrational S₁⇃S₀ transitions; the interval S₂-S₁ has a magnitude of about 1300 cm⁻¹. Reported at the VIIIth International Conference on the Spectroscopy and Chemsitry of Poprhyrins and Their Analogs, Belarus, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 79–85, January–February, 2000.     

Vibrational spectra of p-chlorobenzaldehyde and its deuterated derivatives

The vibrational modes of parachlorobenzaldehyde are assigned using infrared and Raman spectra, valence force field calculations of normal coordinates, and deuteration effects. Low temperature and isotopic studies show that the band at 310 cm^?1 previously observed as a single band is a closely spaced doublet. One component is assigned as the out-of-plane CCl wagging mode, the other as a mixed CClCHO in-plane bending deformation. A feature of the spectra in all the isotopic parachlorobenzaldehydes is an intense doublet in the 1700 cm^?1 region interpreted as Fermi resonance between a combination band and the carbonyl stretching mode.     

The photoelectron spectra of cyclooctatetraene and its hydrogenated derivatives

The photoelectron spectrum of cyclooctatetraene (COT; 1) has been re-examined. Correlation with the spectra of the dihydro- (2, 3), tetrahydro- (4, 5, 6), hexahydro- (7) and octahydro- (8) derivatives confirms the orbital sequence originally proposed by Eland, namely 5a₁ (π), 7e (π), 4b₂ (π), σ. It is shown that the positions and the relative spacing of the π-orbitals are the result of a competition between through-space and through-bond interactions.The photoelectron spectroscopic results for the hydrogenated derivatives of COT yield information about their conformation; in particular about the twist angles between consecutive π-bonds. The spectrum of 1,5-cyclooctadiene (6) confirms that this molecule preferentially adopts the boat conformation.An empirical rule is proposed which yields estimates for the orbital energies of basis π-orbitals in monocyclic hydrocarbons.     

IR spectra of benzaldehyde and its derivatives in different aggregate states

We have measured the IR Fourier-transform spectra of biologically active benzaldehyde and its derivatives in the gas and liquid phases. For compounds of this class, the role played by C=O, OH, and CH groups in intra- and intermolecular has been analyzed. We have revealed spectral features that characterize the participation of C=O groups of unsubstituted benzaldehyde molecules in the occurrence of intermolecular hydrogen bonds C=O...H-C with the formation of molecular dimers of different types. For 2-hydroxybenzaldehyde molecules, spectral data have been obtained that are indicative of the occurrence of intramolecular hydrogen bonds of the C=O...H-C type in solutions. In 2-methoxybenzaldehyde molecules, no intramolecular hydrogen bonds have been observed.