Theoretical calculations B3LYP

Theoretical calculations (B3LYP/6-31G ) were reported for geometries (bond lengths and bond angles) and chemical shifts of 3-methyl- and 3-phenyl-4-hydroxy-2-oxo-2/7-pyrido[2,l-f>][l, 3]oxazinium inner salts (00JCS(P2)2096). 

IR spectra in conjunction with theoretical calculations (B3LYP/6-31G ) indicate that the n /2ydro-(2-hydroxy-4-oxo-4//-pyrido[l, 2-n]pyrimidinium)-hydroxide form exists in solution and in the crystal, but the 2-hydroxy-4//-pyrido[l,2-n]pyrimidin-4-one tautomer dominates in the gas phase (00JCS(P2)2096). 

The one-electron oxidation of 1,2-dithiin 20 with 1.5 equivalent of SbCl5 under vacuum at room temperature gave a bright yellow solution that exhibited a nine-line ESR signal. The optimized structure obtained by theoretical calculations (B3LYP/6-31G(d)) for the radical cation 20 + was the one with a... 

The other half of the isomerization takes place directly bypassing a trappable intermediate, as recently confirmed by extensive theoretical calculations [B3LYP, CASPT 2, (8/8)CASSCF] [145],... 

Electronic Effects. Theoretical calculations (B3LYP/6-311 + G // B3LYP/6-31G ) of a series of substituted phenylcarbenes (PCs, 1) give more... 

Theoretical calculations (B3LYP/6-31G ) indicated that in their 13C NMR spectra C(2) and C(9) carbons of anhydro-(2-hydroxy-4-oxo-4H-pyrido[ 1,2-a]pyrimidinium)hydroxide mesoionic forms appeared at significantly higher field (ca. 159-160 ppm and 115-116 ppm, respectively), than in the 2-hydroxy-4/7-pyrido[l,2-a]pyrimidin-4-one tautomers (ca. 169— 173 ppm and 130 ppm, respectively) (00JCS(P2)2096). C(8) carbon of mesoions (pyridine-)/ type carbon) appeared at lower field (144-146 ppm) than 6-C (140 ppm, pyridine-a type carbon), as is typical of pyridinium compounds. 

By theoretical calculations (B3LYP/6-31G ) four reaction pathways were investigated formation of endo or egzo product with initial bond formation to C2 or C3 in indole. For each mechanism theoretical 13C KIE were analysed and the best agreement of theoretical and experimental KIEs was found for the reaction involving the intermediacy of the radical cation 11, resulting from electrophilic aromatic substitution of indole at C3 by cyclohexadiene in the rate-limiting step ... 

The differences in deuterium and carbon isotope effects indicate the asymmetric transition state with more advanced carbon-carbon bond formation to the terminal Cl atom. The difference between deuterium isotope effects for HCI-S and Htmns hydrogens probably originates from experimental uncertainty. Theoretical calculations (B3LYP/6-31G, B3LYP/6-311+G ) for carbene addition to 1-butene were carried out for two modes with carbene approaching carbon atom Cl or C2. The best agreement for experimental isotope effects is for carbene attack on terminal carbon atom and the carbene-alkene separation in the transition state of 2.5 A. 

In theoretical calculations (B3LYP/6-31G) different catalyst conformations and alkene orientation were taken into consideration. The best agreement of experimental and predicted isotope effects were achieved for asynchronous transition state with oxygen atom distances of 2.32 and 1.99 A to carbon atoms 1 and 2, respectively. 

Unreacted cyclohexanone, isolated from reactions taken to 83% and 89% conversion was analysed by 13C NMR and experimental isotope effects were calculated. For theoretical calculations (B3LYP/6-31+G /PCM) DBU was replaced... 

Theoretical calculations (B3LYP) gave predicted isotope effects consistent with experimental effects. Modelled reaction pathway involves complexation of the diazoesters to rhodium, loss of N2 and rhodium carbenoid formation and formation of asynchronous but concerted cyclopropanation transition state. 

Diazoimidazoles were reported to be light sensitive (CHEC-II(1996)). Stepwise controlled fragmentation photolysis in carbon monoxide-doped argon matrices of 4-diazo-4/7-imidazole was reported, and FT-IR characterization of each fragmentation step in Scheme 44 was in accord with theoretical calculations [B3LYP/6-3111G(d,p)] <2000EJ02535>. 

Summary The synthesis of the first silicon complexes with the tridentate diketoamine HN[CH2C(rBu)=0]2 (1) is described. The reaction of YSiXs (X = Cl, Br Y = H, Cl, Br, Ph, Vinyl) with 5-aza-2,2,8,8-tetramethylnonane-3,7-dione (1) in the presence of NEtj as an auxiliary base furnished the unusual dinuclear silicon complexes (6-11) having pentacoordinate silicon centers. Theoretical calculations (B3LYP/6-31G ) carried out for the monomeric chloro-substituted silane 7A are consistent with a folded structure and a relatively short and highly polarized Si-N bond (1.742 A Charge Si 0.96 N -0.53). The calculated value for the dimerization energy of 7A is -29 kcal/mol, reflecting the presence of a partial Si-N it-bond. Thus, the novel dimeric silicon compound 7 is the result of a head-to-tail dimerization of formally two Si=N bonds in 7A. 

Theoretical calculations (B3LYP/lanl2dz) showed that the spl conformer of the POME pendant is less polar than the sp2 (2.77 versus 3.47 D). Correspondingly, spl predominates in low and medium polarity solvents and induces a preference for the... 

Theoretical calculations (B3LYP/6-31G(d)) for the ring-opening transition states of the oxetene reveal that the transition state to the E-form (TSE) is 8.3 kJ/mol more stable than the transition state to the Z-form (TSZ). In addition, the natural bond... 

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