Protonation of pyrrolo [1,2-α] Pyrimidine derivatives

The protonation of pyrrolo [1,2-] pyrimidine and 6, 7, 8, 9-tetrahydropyrimido [1, 2-] indole derivatives in CF₃COOH (at –15 to +25° C) and in CF₃COOH/H₂SO₄ (at 25°) was studied by PMR spectroscopy. The investigated compounds form monocations, the structure of which corresponds to the addition of a proton to the carbon atom of th pyrrole fragment in the position to the bridge nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 686–692, May, 1976.     

Quinoxaline N-oxide ion radicals. 2. Structures of anion radicals of N-oxides of hydroxymethyl derivatives of quinoxaline and products of their electrochemical reduction

The redox properties of 1,4-dioxides of hydroxymethyl and formyl derivatives of quinoxaline were studied by means of EPR spectroscopy and polarography. The electrochemical reduction of the 1,4-dioxides proceeds in several steps with successive deoxidation and the formation of dianions of substituted quinoxalines and is also accompanied by an intramolecular redox process. The experimentally observed hfs constants in the EPR spectra of the anion radicals formed in the reduction are in agreement with the corresponding values calculated by the INDO method.See [1] for communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1412–1416, October, 1985.The authors thank I. A. Abronin for his assistance in performing the quantum-chemical calculations.     

Electronic structure,PMR spectra,and alkylating capacity of some 2- and 6-alkoxypurines

The simple MO LCAO method was used to calculate the isomeric N,N-dimethylhypoxanthines and the corresponding 2(6)-ethoxy- and 2(6)-ethoxy-8-chloro derivatives, and the PMR spectra of a number of compounds of this type were measured. A qualitative correlation was observed between changes in the -electron densities and changes in the chemical shifts of the protons of the N-methyl groups. Factors affecting the alkylating capacity of 2(6)-alkoxypurines and the direction of the reaction of these compounds with sodiomalonic ester when the molecules contain two different reaction centers were examined. The use of the -electron densities and orders and polarizabilities of the heterocycle — substituent bonds as reactivity indexes makes it possible to explain the highest alkylating capacity of 2-ethoxy-3,7-dimethylhypoxanthine and its 8-chloro derivative and the order of other compounds with respect to this capacity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 265–271, February, 1971.     

Effect of the medium on the reaction of 4-methyl-7-azaindoline with acetic and trifluoroacetic acids

The effect of the medium on the equilibrium involved in proton transfer via a hydrogen bond and dissociation of ion pairs in systems composed of 4-methyl-7-azaindoline and acetic and trifluoroacetic acids was examined by means of PMR and IR spectroscopy. The position of the molecular H complex ? ion pair equilibrium depends on the proton-donor-acceptor properties of the solvent and is shifted to favor the ionic form in the order CH₃CN < CH₂Cl₂< CDCl₃. A change in the dielectric constant of the medium affects mainly the degree of dissociation of the ion pairs.     

Indolizines. 6. Relative reactivities of isomeric 6-, 7-, and 8-ethoxycarbonylindolizine derivatives

The kinetics of the alkaline hydrolysis of 2-phenyl-6-, -7-, and -8-ethoxycarbonylindolizines were studied. The rate constants for the hydrolysis of these compounds and the indexes of the dissociation constants of 2-phenylindolizine-6-,-7-, and -8-carboxylic acids were determined by spectrophotometry. The indexes of the electronic structures and reactivities of 2-methyl-6-, -7-, and -8-ethoxycarbonylindolizines were calculated from theory.See [1] for Communication [5].Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 627–633, May, 1979.     

PMR spectra of protonated pyrazine and quinoxaline N-oxides

The dependence of the chemical shifts of the protons of quinoxaline and quinoxaline and pyrazine N-oxides and N,N-dioxides on the acid concentration was studied. The changes in the PMR spectra on passing from the neutral bases to the monocations were examined. The first protonation of pyrazine and quinoxaline N-oxides occurs at the N₄ nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 846–852, June, 1971.     

PMR spectra and electronic structures of the neutral bases and cations of thiazolo [3,2-a] -benzimidazole and its methyl derivatives

The PMR spectra of the neutral bases and cations of methyl derivatives of thiazolo[3,2-a]-benzimidazole were studied. The dependence of the chemical shifts on the acid concentration was examined. The investigated system is protonated and N-methylated at the N₉ atom. The structure of the conjugated cation corresponds to considerable delocalization of the effective positive charge to the heteroatoms of the thiazole ring. A satisfactory linear correlation between the corrected chemical shifts and the -electron densities, calculated by the simple MO LCAO method using a coulombic integral for the sulfur atom, h_S=0.9, and the parameters of the Pullman system for the remaining heteroatoms, was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 937–945, July, 1971.     

Electronic spectra of quinoxaline 1-N-oxides

The nature of theπ→π ^* transitions in the spectra of quinoxaline 1-N-oxides as compared with unoxidized quinoxalines was examined on the basis of an experimental, study and calculation by the Pariser-Parr-Pople configurational interaction method.