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CBS-QB3 methods

The rate-determining step of this second reaction mechanism is the isomerization of the cyclic diradical to tropone, since the TS connecting the intermediate to the final product lies 84.0 kcal/mol (from CBS-QB3 method) above the starting o-QM. [Pg.59]

The unimolecular reactions of CH3CH2CH2O2 were studied in detail (Fig. 6) complete potential energy surfaces were generated using both DFT [B3LYP/ 6-31+G(d,p) and mPWlK/6-31+G(d,p)] and CBS-QB3 methods. As expected, 1,5-H transfer [Equation (34)] occurs with the lowest barrier, followed by simultaneous 1,4-H transfer and HO2 expulsion [Equation (31)]. The overall decompositions of each H-atom transfer product (i.e., each QOOH radical) were modeled. It... [Pg.95]

The CBS methods are available as keywords in the Gaussian program. The CBS-Q, CBS-q, and CBS-4 methods are incorporated in Gaussian 9475 and later versions. The CBS-QB3 method is available in Gaussian 98."... [Pg.177]

A similar pattern is seen for the two isomers of 1,3-diazetidine. For example, (1) for the trans-isomer, the CBS-QB3 method shows two variances from the monotonically increasing frequencies (2) because of their symmetries (both molecules have a C2 axis), many of the vibrations of both the conformers are predicted to have a very low or exactly zero intensity and (3) only half or less of the 24 normal modes of vibration have significant intensity. [Pg.637]

Activation energies of pericyclic reactions Performance of DFT, MP2, and CBS-QB3 methods for the prediction of activation barriers and reaction energetics of 1,3-dipolar cycloadditions, and revised activation enthalpies for a standard set of hydrocarbon pericyclic reactions ... [Pg.230]

Three functionals, B3PW91, MPW1PW91, and PBEIPBE in combination with 6-31-l-G, 6-311-l-G and AUG-cc-pVTZ basis sets were used in a DFT study of the one-electron reduction of CF3X (X = Br, Cl, I) accompanied by C-X bond dissociation. The dissociation energies and electron affinities were compared with results obtained with the Gn and CBS-QB3 methods. ... [Pg.156]

Gimer V, KhuongKS, Leach AG, Lee PS, BartbergerMD, HoukKN A standard set of peri-cyclic reactions of hydrocarbons for the benchmarking of computational methods the performance of ab initio, density functional, CASSCF, CASPT2, and CBS-QB3 methods for the prediction of activation barriers, reaction energetics, and transition state geometries, / Phys Chem A 107(51) 11445—11459, 2003. [Pg.74]

Pathways and reaction barriers for the unimolecular decomposition of MB were explored with CBS-QB3 methods by El-Nahas et al. in 2007. Ah and Vioh " have recendy used ab initio and DFT methods to reexamine MB decomposition. Their bond energies and reaction barriers were generally in good agreement with those of El-Nahas. They have used the computations to compute high-pressure and pressure-dependent kinetics for 10 possible decomposition pathways. They noted the importance of entropic factors in addition to the energetics in determining the kinetics. [Pg.131]


See other pages where CBS-QB3 methods is mentioned: [Pg.177]    [Pg.313]    [Pg.321]    [Pg.482]    [Pg.483]    [Pg.637]    [Pg.302]    [Pg.202]    [Pg.282]    [Pg.475]    [Pg.247]    [Pg.253]    [Pg.403]    [Pg.574]    [Pg.201]    [Pg.52]    [Pg.133]   
See also in sourсe #XX -- [ Pg.156 ]




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