Solvatochromism of Heteroaromatic Compounds: XXVI. Solvent Effect on the Solvatochromic Parameters of IR Bands of <Emphasis Type="Italic">N</Emphasis>-Methylanilines and Related Hydrogen Bond Donors

Formation of a hydrogen bond between molecules of a proton donor (phenol, pyrrole, N-methylanilines) and a solvent decreases the sensitivity of the XH stretching frequency to the polarity/polarizability of solvents. A change in the bond configuration in the amine moiety of N-methylaniline and related compounds upon formation of a solvation H complex is manifested in that the absolute terms of the solvatochromic equations for inert and protophilic media are different. The spectroscopic effect from the geometric reorganization of molecules is determined by their structure and the capability to act as hydrogen bond donors. Multicentered hydrogen bond with π bases affects the geometry of the amine fragment of N-substituted anilines to a lesser extent than does two-centered H bond with onium bases.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 642–649.Original Russian Text Copyright © 2005 by Vokin, Oznobikhina, Shulunova, Ustinov, Bozhenkov, Levkovskaya, Turchaninov.For communication XXV, see [1].     

Solvatochromism of Heteroaromatic Compounds: XII. Solvatochromism and Tautomerism of 4-Methyl-3-nitro-1,2,4-triazol-5-one in Aprotic Solvents

The long-wave absorption band in the UV spectrum of 4-methyl-3-nitro-1,2,4-triazol-5-one is highly sensitive to specific solvation by hydrogen bonding with a protophilic solvent. The UV and IR spectra suggest that the compound mainly exists in the form of the N¹H tautomer. The qualitative and quantitative relationships characterizing the solvent effect on the spectral characteristics of the major tautomer were elucidated.     

Solvatochromism of Heteroaromatic Compounds: X. 2-Phenylpyrrolide Anion

2-Phenylpyrrolide anion was obtained in high-polarity media containing MeONa as an ionizing agent. The bathochromic shift of the long-wave absorption band in going from the neutral to deprotonated form is explained by the difference in the molecular orbital characteristics of the parent molecule and the anion, as well as the by change in the equilibrium conformation on deprotonation. According to ab initio calculations, the conformational rearrangement contributes partly to the observed shift; the greatest contribution is from the destabilization of the highest occupied molecular orbital.     

Solvatochromism of Heteroaromatic Compounds: XV. 3-Nitro-1,2,4-triazol-5-ones

Effect of the medium on the parameters of the long-wave absorption band in the electronic spectra of H complexes formed by 3-nitro-1,2,4-triazol-5-one and its N-methyl derivatives with aprotic protophilic solvents was described on a quantitative level using Kamlet-Taft solvatochromic parameters. A weak nonadditivity was revealed in the influence of two kinds of intermolecular hydrogen bonds.     

Solvatochromism of Heteroaromatic Compounds: IX. Anions of 3-Nitro-1,2,4-triazol-5-ones

Solvatochromism of the long-wave band in the electronic absorption spectra of 3-nitro-1,2,4-triazol-5-one anions was studied and quantitatively described with the Kamlet-Taft solvent parameters. Azole anions are specifically solvated in amphiprotic solvents. The strength of the hydrogen bond in H complexes with amphiprotic solvents decreases in going to the Franck-Condon excited state. The UV and IR specrta show that 3-nitro-1,2,4-triazol-5-one anions, in contrast to nitroazole anions, are specifically solvated with participation of the carbonyl group. In highly polar organic solvents the 3-nitro-1,2,4-triazol-5-one anion mainly exists in the form of the 1H tautomer.     

A study of photoelectron spectra in the framework of the semiempirical AM1 method

The characteristics of photoelectron (PE) spectra of 2-phenylpyrroles and biphenyls have been correlated with the UV spectroscopy data for their radical cations. The geometric and electronic structures of the compounds and radical cations have been calculated using the AM1 method. The absorption bands of the radical cations observed in the visible region of spectrum have been found to pertain to the quasi-Koopmans type,i.e., they are realized between the doubly and partially occupied -MO, but their energies differ strongly from those calculated on the basis of PE spectra. This is explained by the distinction between the spatial structure of a molecule and that of the respective radical cation. The second cause of the discrepancy between the data of the two spectral methods consists in orbital — interactions, which are most conspicuous in the case of 4(4)-halogen-substituted compounds.For Part 4 see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 869–874, May, 1993.     

Solvatochromism of Heteroaromatic Compounds: XIX. Factors Affecting Quantitative Characteristics of Solvatochromism in Aprotic Inert Media

The effects of aprotic inert media on the electronic absorption spectra of aromatic nitro compounds p-NO₂C₆H₄R were used as evidence for the linear correlation between the slope s _a of the solvatochromism equations _max = ₀ + s _a^* and the dipole moments of the molecules in their ground electronic state _g. A linear correlation was established between 0 and the first ionization potential of subunits C₆H₅R. A new approach to estimating the dipole moment of electronically excited molecules (_e) for molecules like p-NO₂C₆H₄R on the basis of the correlation _e = r_g was proposed.     

Electron spectra of radical cations of heteroanalogs of indene

The electron absorption spectra of the radical cations of indene heteroanalogs were studied by nanosecond laser photoexcitation. The absorption bands in the 450–650 nm region were assigned on the basis of absorption and photoelectron spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 750–752, June, 1985.     

Solvatochromism of Heteroaromatic Compounds: VIII. 2-(Tricyanovinyl)-5-phenylpyrrole

Rotational isomerism of 2-(tricyanovinyl)-5-phenylpyrrole and formation of complexes with a three-centered (bifurcational) hydrogen bond were studied by UV spectroscopy and quantum-chemical calculations. In the gas phase and in weakly and moderately protophilic media these compounds have mainly the syn-periplanar form stabilized by the intramolecular hydrogen bond involving the orthogonal system of the nitrile group and the NH hydrogen atom. No intermolecular H complex is formed in such solvents. In tetrahydrofuran, cyclohexanone, pyridine, and some other media a complex conformational equilibrium is observed. Interaction with aliphatic alcohols, amides, dimethyl sulfoxide, and triethylamine results in stabilization of the H complex of the anti-periplanar conformer.