DFT studies B3LYP

Figure 13 illustrates the novel result of N20 formation, isomerization and release, as predicted by the theoretical calculations. Figure 14a shows a DFT study (B3LYP) of the reaction profile [Eq. (11)], allowing to characterize intermediates on the potential hypersurface. It can be seen that the initially formed r 2-N20 complex isomerizes to the linear... 

The success in a simple model system encouraged Feldgus and Landis to study the fuller DUPHOS-based system for enantioselective hydrogenation (as defined in Fig. 31.9) [45]. ONIOM methods were required because of the level of complexity a core of the rhodium-complexed atoms was treated by DFT at B3LYP level, the core organic atoms at Hartree-Fock level, and the remainder by... 

The density functional methods assessed in this study (B3LYP, BLYP, and LDA) all perform much worse for the enthalpies of formation of the larger molecules in the G3/99 set. This is due to a cumulative effect in the errors for the larger molecules in this test set. The errors are found to be approximately proportional to the number of pairs of electrons in the molecules but the methods are not improved significantly when a higher-level correction such as that used in G2 or G3 theory is added the DFT methods. Further correction schemes may be necessary to improve the performance of density functional methods for large molecules. 

Subsequently, DFT methods (B3LYP functional ) were employed to compute (1) natural charges from which changes in charges are mapped out for comparison with the NMR-based conclusions, (2) GIAO-NMR to predict the chemical shifts for comparison with the experimental results, and (3) nuclear-independent chemical shift (NICS) in order to evaluate relative aromaticity in different rings. Finally, solvent effects were estimated by the polarized continuum model (PCM). In selected cases, parallel DNA-binding studies (with MCF-7 human mammary... 

The present level of theoretical work can be seen in a recent paper by Sevilla s group. They have employed DFT to study the details of proton transfer reactions in Gua Cyt base pairs [57]. Using the DFT functional B3LYP with the 6-31 + G(d) basis set on the entire Gua Cyt molecule (19 heavy atoms), the results are presented which show that it is energetically favorable for the N1 proton of guanine to transfer to the N3 of cytosine after reduction of cytosine or after oxidation of guanine. 

In another DFT study, the reductive decomposition of artemisinin 9a was investigated by the DFT B3LYP method, together with the 6-31G(d) and 6-31- -G(d,p) basis sets <2006BMC1546>. 

Fluoro-o-benzyne (41) has also been isolated in cryogenic matrices by photolysis of the corresponding phthalic anhydride. The C=C stretching vibration of 41 has been observed at 1866 cm Compared to the parent, the triple bond length is only modestly increased according to DFT calculations (Fig. 16.2). Note, however, that the observed frequency shifts upon fluorine substitution in 4 are not reproduced at the B3LYP or BLYP level of theory (Fig. 16.2). Thus, the performance of different DFT functionals to account for the properties of o-arynes still remains a matter of debate,and casts some doubts on the results of certain DFT studies. 

We also performed extensive DFT studies on both the full target system and the model for calibration purposes. For details of one-electron basis sets used please consult Ref. (55). We used the B3LYP functional but found the ground-state potential energy surface to be relatively insensitive to the chosen functional (note though that this does not mean that DFT gives the correct surfaces, as important nondynamical correlation effects are... 

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