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51.
N. M. Vitkovskaya V. B. Kobychev A. B. Trofimov B. A. Trofimov 《Russian Chemical Bulletin》1997,46(10):1677-1682
The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated
by theab initio (RHF/4-31G) method. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide
ion and between the corresponding carbanions and water were found on the pontential energy surfaces of the proton transfer
reactions. There are no transition states with energies exceeding the energies of the initial reagents or those of the end
products on the reaction coordinate. Therefore, the expenditure of energy to overcome the barriers is completely compensated
by the energy gain due to the formation of intermedite complexes. The direction of multiple bond migration by this mechanism
is almost completely determined by the ratio of the energies of the initial reagents and the end products. Account of the
electron correlation and the extension of the basis set do not lead to radical changes in the results.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1772–1777, October, 1997. 相似文献
52.
Vladimir B. Kobychev Nadezhda M. Vitkovskaya Irina L. Zaytseva Elena Yu. Larionova Boris A. Trofimov 《International journal of quantum chemistry》2002,88(5):542-548
Quantum chemical analysis (MP2/6‐31+G*) of the pyrrole anions addition to carbon disulfide and the substitution effects therein shows that pyrrole‐2 (5)‐carbodithioates are thermodynamically the most stable compounds, while 1‐isomer obtained from the unsubstituted pyrrole is likely a kinetic product. Steric hindrances destabilize N‐adducts when a methyl substituent appears in a 2(5) position and the 2,5‐dimethyl‐1‐pyrrolecarbodithioate anion turns out to be even less stable than the 2,5‐dimethyl‐3‐pyrrolecarbodithioate anion. By contrast, pyrrole‐1‐carboxylates are calculated to be the most stable adducts of CO2 with pyrrole anions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
53.
Bellini G Benziger J Bick D Bonetti S Bonfini G Buizza Avanzini M Caccianiga B Cadonati L Calaprice F Carraro C Cavalcante P Chavarria A D'Angelo D Davini S Derbin A Etenko A Fomenko K Franco D Galbiati C Gazzana S Ghiano C Giammarchi M Goeger-Neff M Goretti A Grandi L Guardincerri E Hardy S Ianni A Ianni A Kobychev V Korablev D Korga G Koshio Y Kryn D Laubenstein M Lewke T Litvinovich E Loer B Lombardi F Lombardi P Ludhova L Machulin I Manecki S Maneschg W Manuzio G Meindl Q Meroni E 《Physical review letters》2011,107(14):141302
The rate of neutrino-electron elastic scattering interactions from 862 keV (7)Be solar neutrinos in Borexino is determined to be 46.0±1.5(stat)(-1.6)(+1.5)(syst)?counts/(day·100 ton). This corresponds to a ν(e)-equivalent (7)Be solar neutrino flux of (3.10±0.15)×10(9) cm(-2)?s(-1) and, under the assumption of ν(e) transition to other active neutrino flavours, yields an electron neutrino survival probability of 0.51±0.07 at 862 keV. The no flavor change hypothesis is ruled out at 5.0?σ. A global solar neutrino analysis with free fluxes determines Φ(pp)=6.06(-0.06)(+0.02)×10(10) cm(-2)?s(-1) and Φ(CNO)<1.3×10(9) cm(-2)?s(-1) (95% C.L.). These results significantly improve the precision with which the Mikheyev-Smirnov-Wolfenstein large mixing angle neutrino oscillation model is experimentally tested at low energy. 相似文献
54.
In the framework of the MP2/6-311++G**//RHF/6-31G* ab initio approach we investigated the structure and relative stability of the imine (-CHR-CH=N-) and enamine (-CR=CH-NH-) forms of the simplest imines, oximes, and their ethers. Although the enamine form is unstable, double bond migration R2CH-CH=N-→ R2C=CH-NH-is often regarded as one of the stages of a series of reactions that take place in superbasic media, in particular, synthesis of pyrroles from ketoximes and acetylene. For isomerization of E-ethaneimine CH3-CH=NH to vinylamine CH2=CH-NH2, calculations predict an increase of 4.3 kcal/mol in energy. A close value (4.8 kcal/mol) was obtained for the energy of isomerization of ketimine (CH3)2C=NH to 2-aminopropene. The methyl group in CH3-CH=CH-NH2 stabilizes the neighboring double bond, and the transformation of E-propane-1-imine into E-and Z-aminoprop-1-ene is accompanied by an increase of 2.8 kcal/mol in energy. After the transition from imines to oximes, the enamine form is drastically destabilized. The highly endothermal character of the CH3-CH=NOH → CH2=CH-NHOH rearrangement (16.4 kcal/mol) is retained from acetaldoxime to its methyl ether and decreases by only 1.0 kcal/mol for the isomerization reaction of the vinyl ether of acetaldoxime to N,O-divinylhydroxylamine. These rearrangements are thermodynamically unfavorable probably because of the increased negative charge on the nitrogen atom and, as a consequence, destabilization of the N-O bond. 相似文献