IR spectra of pyrimidine carboxylic acids and some problems involving their structure

The IR spectra of solid pyrimidinecarboxylic acids and of solutions of them in dioxane and chloroform were obtained. It is demonstrated that the frequencies of the stretching vibrations of the carboxyl C=O groups of acids that are not capable of tautomerism correlate linearly with their acidity constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 833–835, June, 1972.     

A study of the possible and preferred site of protonation in 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene by vibrational spectroscopic methods

The normal co-ordinate analysis have been carried out for 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene (MTBD) and its three possible protonated tautomeric forms. The calculations and measured infrared (IR) spectra are consistent with a tautomeric species in which the proton is attached to an imine nitrogen atom.     

Rate and Equilibrium Constants for Reactions Transferring a Dimethylcarbamoyl Group between Pyridines

We have studied 18 reactions, including four identity reactions, involving transfer of a dimethylcarbamoyl group with N-acylpyridinium bonds to pyridine and its 4-substituted derivatives in acetonitrile solutions at 298 K. The rate constants k _ij varied within the range 0.4 to 10^–6 L/mol·s; the equilibrium constants K _ij varied from 10⁷ to 10^–5. The rate and equilibrium for exchange of carbamoyl groups are described satisfactorily by the Brönsted equation. We have shown that all the reactions occur according to a forced concerted S _N2 mechanism. The structure of the transition state and its position on the reaction coordinate for identity transfer are considered using a More O'Ferrall-Jencks diagram.     

Rate and Equilibrium of Acetyl Group Exchange between Pyridines and Pyridine N-Oxides

22 Acetyl group exchange reactions between N-acetoxypyridinium salts and 4-dimethylaminopyridine, 4-morpholinopyridine, and N-methylimidazole in acetonitrile at 298 K have been studied. The rate constants varied from 10⁵ to 10^–4 L/mol·s, and the equilibrium constants ranged from 10⁹ to 10^–9. The rates and equilibrium constants of these reactions did not comply with the Brönsted equation. The kinetics of the acetyl exchange reactions are well described by a correlation equation containing squared terms.     

Basicity constants of natural isoflavonoids

The basicities (pK_BH+) of 13 natural isoflavones have been determined spectrophotometrically in sulfuric acid solutions. It has been shown that the change of basicity in this series of compounds depends on the geometry of the molecules and on intramolecular effects.     

1,3,5-Triaryl-Δ2-pyrazolines with a nitro or amino group in the N-phenyl ring

A number of p-nitrophenylhydrazones of chalcones and 1-(p-nitrophenyl)- and 1-(p-aminophenyl)-3-aryl-5-phenyl-2-pyrazolines were synthesized, and their UV and IR spectra were measured. It is shown that the direction of polarization in the system of the ground and first excited states of the pyrazolines depends substantially on the character and position of the substituents introduced; the experimental data are compared with the results of calculation of the electronic states of the molecules by the Pariser-Parr-Pople (PPP) method. It was established that the nitro compounds have luminescence properties and that their absorption spectra in inert solvents have a vibrational structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1538–1543, November, 1977.     

Investigation of azomethine group vibrations in aromatic schiff bases and their N-oxides by vibrational spectroscopy methods

The effects of fluorine substitution in benzene rings and quaternization of the nitrogen atom in Schiff bases of the general formula R−CH=N−R′ on the vibration characteristics of the azomethine group are analyzed. Normal vibrations and intensities of IR bands are calculated. It is shown that the spectroscopic behavior of the C=N bond is almost independent of the electronic effects of substituents in the benzene rings of the molecules studied, and the changes in the intensities of ν_C=N bands are caused by interactions between vibrations. This points to the stability of this bond in the series of molecules under consideration. For diphenylnitrones, N→O vibrations are identified. L. M. Litvinenko Institute of Physical Organic Chemistry and Carbon Chemistry. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 310–315, March–April, 1995. Translated by L. Smolina     

Rate and equilibrium constants of transfer of the dimethylcarbamoyl group between substituted pyridines and their N-oxides

Transfer of the dimethylcarbamoyl group from N-acyloxypyridinium salts to pyridines and from N-acylpyridinium salts to pyridine N-oxides was studied in acetonitrile. Equations relating the reaction rates and equilibria in the N-O and O-N acyl transfer series to the basicity of the nucleophile and leaving group were obtained. The reactions all are one-stage and occur by the forced concerted SN2 mechanism. The intersecting state model was used to obtain a modified Marcus equation that accounts for the asymmetry of the transition state with respect to reagents and products and allows uncontradictory analysis of the reaction mechanism.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1720–1727.Original Russian Text Copyright © 2004 by Rybachenko, Shreder, Gokhfeld, Chotii, Kovalenko, Lenska.This revised version was published online in April 2005 with a corrected cover date.     

Interpretation of Π→Π electronic transmissions in the absorption spectra of flavone and its hydroxy derivatives

The electronic spectra of flavone and its 4′-, 3-, 5-, and 7-monohydroxy derivatives have been calculated by the standard Pople-Pariser-Parr method. The contributions of the fragments to the total molecular excitation have been calculated. It has been shown by computer modeling that the electronic transitions of the flavone spectrum can be reduced to the corresponding transitions of the spectrum of chromone, but not of chalcone. A graphical analysis has been performed of the experimental absorption curves. A four-component system of individual bands in the 230–400 nm region is proposed. Their mutual superposition or resolution is responsible for the features of the spectra of hydroxy-substituted flavones.