Quantum chemical calculations of energies, electronic structures, and molecular geome tries of 3,5,6 trimethylthieno[2,3 d]pyrimidin 4 one (1), tricyclic 2,3 tri , 2,3 tetra , and 2,3 pentamethylene substituted 5,6 dimethylthieno[2,3 d]pyrimidin 4 ones (2-4), carboxy lic acids 5-8 resulting from oxidation of compounds 1-4 at the methyl group in position 5 of thienopyrimidine, methyl esters of these acids (9-12), and products of ipso nitration of esters (13-16) were performed in terms of the HF and DFT (B3LYP) approximations with the 3 21G basis set. Also, calculations for mixed anhydrides of nitric acid and carboxylic acids 17-20 were carried out. The possible causes of differences in the behaviors of 3 unsubstituted and 3 substituted thieno[2,3 d]pyrimidin 4 ones were discussed.Key words: thieno[2,3 d]pyrimidin 4 ones, nitric acid oxidation, ipso substitution, quan tum chemical calculations, Hartree-Fock method (HF), DFT/B3LYP 3 21G method.

No abstract

The thermodynamic stability of 1,2 and 1,3 azole molecules, as well as of cationic and bipolar (carbenoid) intermediates in the gas phase and in aqueous solution formed by electro philic substitution (proton as a model electrophile) was compared based on the analysis of quantum chemical calculations performed at the DFT/B3LYP/6 31G(D) level of theory with zero point energy corrections. The differences in the chemical behavior of the isomeric 1,2 and 1,3 azole pairs, viz., pyrazole-imidazole, isoxazole-oxazole, and isothiazole-thiazole, were considered.Key words: 1,2 azoles, 1,3 azoles, electrophilic substitution, quantum chemical calcula tions, DFT/B3LYP/6 31G(D) method.In the previous communication, 1 we considered and discussed the results of quantum chemical calculations of 1,2 and 1,3 azoles, as well as of the intermediates that are formed via two alternative mechanisms of electrophilic substitution: the normal addition-elimination mechanism with the formation of intermediate cationic  complexes and the elimination-addition mechanism specific to azoles with the participation of ylide (carbene) intermedi ates. Such an ylide substitution is especially characteristic of 1,3 azoles; the corresponding experimental data is sum marized in the review. 2 The goal of the present work is to analyze the results of quantum chemical calculations reported previously 1 in or der to determine the relative thermodynamic stability of 1,2 and 1,3 azole molecules, as well as of cationic and bipolar (carbenoid) intermediates formed during electro philic substitution (proton as a model electrophile), and to consider the differences in the chemical behavior of isomeric 1,2 and 1,3 azole pairs: pyrazole-imidazole, isoxazole-oxazole, and isothiazole-thiazole. Structures 1-10, which characterize the transformation of the starting 1,3 and 1,2 azoles 1 and 6 into ylide substitution inter mediates 2-5 and 7-10, are shown in Scheme 1 and those related to the transformation of the same azoles 1 and 6 into the intermediates of the traditional addition-eli mination mechanism (cationic  complexes 11-16) are shown in Scheme 2. Quantum chemical methodIn the present work, we used the results of our quantum chemical calculations 1 done in terms of the density functional theory (DFT) using the B3LYP functional and the 6 31G(D) basis set with zero point energy corrections taking into account solvation effects using the overlapping sphere model (IEFPCM). 3 The appropriateness of this relatively simple DFT method with a modest basis set was justified in the work. 1 Thus, the results of calculations performed with this method for five membered heterocycles containing one heteroatom are in good agreement with the data obtained by ab initio Hartree-Fock and MP2 4,5 methods, which showed the relationship between the substrate selectivity and the ability of the heteroatom to delocalize a posi tive charge (N > O > S) and between the positional selectivity in the electrophilic substitution reaction of pyrrole, furan, and thio phene and the change in the st...

No abstract

No abstract