B3LYP functional hydrogenation

Hirata and Iwata, 1998, extended these studies to linear oligomers and an infinite linear hydrogen fluoride polymer. Also this study substantiates the applicability of the BLYP and B3LYP functionals, for which reasonable agreement with experiment has been found with respect to structure, binding energies and vibrational frequencies of the species explored. 

Del Bene, J. E., Person, W. B., Szczepaniak, K., 1995, Properties of Hydrogen-Bonded Complexes Obtained from the B3LYP Functional With 6-31G(d,p) and 6-31+G(d,p) Basis Sets Comparison With MP2/6-31+G(d,p) Results and Experimental Data , 7. Phys. Chem., 99, 10705. 

MNDO or ab initio calculations (Table 5.3). Further confirmation for the preference of 1,2-addition was established by ab initio calculation of the C-H bond energy in hydrogenated fullerenes [35]. Hybrid density functional theory using the B3LYP functional with the 6-31 G(d,p) basis set leads to the bond energies shown in Table 5.3. The most stable bond is found in 1,2 adducts with a bond energy of 2.86 eV, followed by a bond energy of 2.69 eV in 1,4-adducts. All the other addition patterns such as 1,3 addition or addition to a [5,6] bond lead to less stable C-H bonds (Table 5.3). 

Less optimistic conclusions about the performance of the DFT/PCM scheme were drawn in a study of solvent effect on the optical rotation of (.S )- -mclhy I benzyl amine [67]. The authors compared the optical rotation of this amine measured in 39 different solvents (whenever possible extrapolated to infinite dilusion) with the results obtained by means of IEF-PCM with the B3LYP functional and the aug-cc-pVDZ basis set. They observed substantial discrepancies for many of the hydrogen-bond forming solvents (which is not... 

TABLE 6.2 Theoretical and Experimental Hyperfine Coupling Constants (Gauss) of Hydrogen Nuclei of the Radicals Studied. All the Theoretical Values have been Obtained with B3LYP Functional... 

The Isoprene-Fe(CO)3 Radical Complex Various acyclic 1,3-diene complexes were investigated using the B3LYP functional.160 The radical complexes 1 and 2 are formally derived by abstracting a hydrogen atom from the isoprene-Fe (CO)3 complex (Figure 10.18). 

How can a theoretical method decide between proposed mechanisms, and how can the origin of the enzymatic power be identified This review will try to answer these questions for one particular theoretical approach, the one where an active site model is treated by accurate quantum mechanical (QM) methods. The main idea in the QM active site approach is to make sure that the computational results have the required accuracy. During the last decade the accuracy of density functional methods (DFT) has been dramatically improved, and in particular the hybrid B3LYP functional has achieved a remarkable accuracy [8, 9]. The use of DFT has also made it possible to treat dramatically larger molecular systems than can be done with conventional wave-function methods of similar accuracy. In spite of this important development, DFT models have usually been limited to 50-60 atoms, but more recently systems with more than 100 atoms have been treated efficiently. Still, even 100 atoms is a very small part of the total number of 8,300 atoms in yeast ODCase, not counting hydrogens or surrounding water molecules. Thus a very severe selection has to be made when the enzyme model is set up, and an important task is to select the residues required to solve the mechanism and to analyze all important contributions. 

Density-functional studies of hydrogen-bonded dimers generally found good results with the B3LYP functional provided large enough basis sets (valence triple zeta with polarization functions) were used [B. Paizs and S. Suhai,/ Comput. Chem., 19,575 (1998)]. 

A number of other theoretical studies on the enamide system have been performed to further elucidate the enantioselectivity derived for different substrate-ligand combinations in the Rh(I)-catalyzed hydrogenation. Li and coworkers examined the PES for the [Rh(/ ,/ )-Et-BisP ]Lcatalyzed asymmetric hydrogenation of a-acetamidoacrylonitrile using the B3LYP functional (Scheme 5) [53]. They chose this... 

DFT calculations using the B3LYP function with a 6-3IG basis set gave activation energies within 2 kcal/mol for the suprafacial 1,5-hydrogen shift/ The C-H bond lengths in the transition state were 1.42-1.43 A. 

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