Stabilization of nonclassical types of valence bond orientation at the carbon atom in organoboron compounds

The complete topological structure of the potential energy surface (PES) of methane in the inversion region was studied by theab initio CCD(full)/6-311++G^** method. The necessity of taking into account nuclear motions was shown. Penta- and hexacoordination of carbon atoms in boron-containing organic compounds was investigated by theab initio MP2(full)/6-31G^** and MP2(full)/6-311++G^** methods. The CB₄H₄Li₂, CB₆N₂H₂, and CB₆O₂ systems containing hexacoordinated carbon atoms correspond to rather deep minima on the relevant PES and can be the subject of synthetic studies. According to theab initio calculations, pyramidal boron-containing systems with hypercoordinated carbon atoms, which fulfill the “8e rule,” also correspond to rather deep PES minima and can be detected experimentally. Dedicated to Academician V. I. Minkin on the occasion of his 65th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 786–796, May, 2000     

Cleavage of the N-N bond in 1-substituted indazoles under the influence of aryllithium compounds

Upon reaction with aryllithium compounds (phenyllithium and m-tolyllithium) m-methyl- and 1-isopropylindazoles undergo cleavage at the N-N bond to give N-substituted 2-aminobenzophenones. The heterocyclic ring of 1-isopropyl-3-phenylindazole also undergoes cleavage at this bond under the influence of phenyllithium.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1078–1081, August, 1982.     

Quantum-chemical analysis of the nucleophilic substitution of the bromine atom by the cyano group at the sp-hybridized carbon atom in the methylbromoacetylene molecule

This paper reports on our quantum-chemical analysis of the nucleophilic substitution of the bromine atom by the cyano group in the reaction of methylbromoacetylene with copper cyanide. According to calculations, the reaction can form a four-membered ring containing a copper atom.     

Nucleophilic substitution at the imidoyl carbon atom: intermediate mechanistic and reactivity behavior between carbonyl and vinyl carbon substitution.

Gas-phase nucleophilic substitution reactions at the imidoyl carbon have been investigated using chloride exchanges, Cl- + RY=CHCl right harpoon over left harpoon RY=CHCl + Cl- with Y = N and R = F, H or CH3, at the MP2, B3LYP and G2(+) levels using the MP2/6-311+G geometries. The results are compared with those for the vinyl (Y = CH) and carbonyl (Y = O) carbon substitution. The mechanism and reactivity of substitution at the imidoyl carbon are intermediate between those of carbonyl (SNpi) and vinyl carbon (SNsigma) substitution, which is directly related to the electronegativity of Y, CH < N < O. The prediction of competitive SNsigma with SNpi path for the imidoyl chloride is consistent with the S(N)1-like mechanism proposed for reactions in solution. The important factors in favor of an in-plane concerted SN2 (SNsigma) over an out-of-plane pi-attack (SNpi) path are (i) lower proximate sigma-sigma* charge-transfer energies (DeltaECT), (ii) stronger electrostatic stabilization (DeltaENCT), and (iii) larger lobe size on C(alpha) for the sigma*- than pi*-LUMO despite the higher sigma* than pi* level. The electron correlation energy effects at the MP2 level are overestimated for the relatively delocalized structure (S(N)pi TS) but are underestimated for the localized structure (SNsigma TS) so that the MP2 energies lead to a wrong prediction of preferred reaction path for the vinyl chloride. The DFT at the B3LYP level predicts correct reaction pathways but overestimates the electron correlation effects.     

p-Fluorphenyl group as an indicator of charge on the carbon atom in aromatic compounds

A linear equation is presented for determining, from the chemical shift of¹⁹F in a p-fluorophenyl group, the effective charge of that CH fragment of the original aromatic molecule the carbon atom of which is bonded to the fluorophenyl indicator group. It has been shown that for a cyclic aromatic 6-electron system determination of the effective charges of the CH fragments by quantum-chemical calculations and the evaluation of this charge from the¹⁹F chemical shift of the corresponding p-fluorophenyl substituents lead to coincident results.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2219–2222, October, 1989.The authors are grateful to N. P. Gambaryan for fruitful discussions.     

Organosilicon compounds XIII. Cleavage of the silicon-carbon bond of 2-trimethylsilylbenzothiazole

The high-yield synthesis of 2-trimcthylsilylbenzothiazole is described, and the labile nature of this silicon-helerocyclic bond is proved when cleavage is affected by aldehydes, acid halides, chloro-formates and anhydrides. Justification for this unusual reactivity and further insight into the reaction mechanism is offered.     

Cleavage of the tin-carbon bond in organotin derivatives of barenes under the action of nucleophilic reagents

Conclusions In contrast to ordinary organotin compounds, organotin barene derivatives are readily cleaved at the Sn-C bond under the action of bases.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2084–2086, September, 1967.     

Electrophilic substitution in the benzene ring of indole compounds (Review)

Data on the orientation of electrophilic substitution reactions (nitration, halogenation, acylation, and sulfonation) in the benzene ring of indoles are systematized. The effect of protonation on the direction of substitution is examined. The effects of a pyrrole ring and a substituent in the benzene ring on the orientation reactions are compared.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1181–1199, September, 1980.     

Indolopyridines with a hetero atom at a position of fusion. 6. Electrophilic substitution in indolo[2,1-a]isoquinoline

Nitration, halogenation, azo coupling, aminomethylation, hydroxymethylation, and acylation reactions of indolo[2,1-a]isoquinoline in a neutral or weakly acid medium gave derivatives at the C₍₁₁₎ position (the pyrrole ring). Using nitrosation as an example, it was shown that electrophilic substitution at the benzene ring of the indole fragment can occur in a strongly acid medium.For Communication 5 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 83–89, January, 1994.     

Isokinetic relationships for nucleophilic substitution reactions at the saturated carbon atom. Reactions in aqueous solutions

An isokinetic relationship (IKR) with the parametersT _iso=6145 K and logk _iso=10.622 is valid for nucleophilic substitution reactions at the saturated carbon atom with the participation of anionic nucleophiles in aqueous solutions. The IKR describes the rate constants of the reactions with different anionic nucleophiles, leaving groups, and substituents at the electrophilic reaction center. Similar reactions with neutral nucleophiles, which follow another mechanism, are described by a separate IKR withT _iso=−1232 K and logk _iso=16.226. The reactions of haloforms with hydroxide ion, which proceed by a specific mechanism involving the haloform ionization equilibrium followed by α-elimination of the halide ion, are described by yet another IKR withT _iso=−1463 K and logk _iso=21.057. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 809–814, May, 2000.     

Cleavage of the carbon-carbon bond in α-glycols under the action of bismuth(v) derivatives

Di(tert-butylperoxy)triphenylbismuth and the triphenylbismuth-tert-butyl hydroperoxide system react with 2,3-dimethylbutane-2,3-diol, benzopinacol, butane-2,3-diol, and ethane-1,2-diol with the cleavage of the C−C bond of α-glycol to form carbonyl compounds. Both heterolytic (through formation of cyclic triphenylbismuth glycolate) and homolytic cleavage occur. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1212–1214, June, 1997.