DFT-B3LYP

Fig. 5.3 Variation of the li, 2s, 3s and contributions to the total electron density at the iron nucleus for a collection of iron complexes. Nonrelativistic B3LYP DFT calculations with the CP (PPP) basis set (taken from [19])...

TABLE 10.1 Typical Accuracy for B3LYP DFT Calculations on Small Molecule Test Sets"... 

A typical demonstration of the utility of theoretical calculations in the assignment of uncertain signals is reported by Quin et al.30 31 As already found by Bagno,116 the experimental values reported in the literature for S-methyltetrahydrothiophenium salt 1, 750 ppm (referred to CS2), did not fit well with the scaled values, calculated by the B3LYP DFT approach and the EMPI method, which were 87.4 and 121 ppm respectively. With the aid of AIM calculations, it was verified that this discrepancy cannot be ascribed to intermolecular interactions in solution, neither salt formation nor interaction with counterions. The experimental redetermination of chemical shift values has given a value of 95 ppm (ext. ref. CS2), in agreement with calculated values. For S-methylthianium ion 16, a value of 68 ppm has been calculated, compared to an experimental value reported in the literature of 670 ppm.29... 

Some effort has gone into prediction and verification of structural parameters of complexes from interaction of HX with thiirane <2004SAA1883>. By means of ab initio MO and B3LYP DFT at the 6-311++(d,p) level, Araujo and co-workers obtained structural and electronic parameters for HF and HCl complexes with thiirane. The complexes have CS symmetry with the HX unit lying in a plane perpendicular to the plane of the thiirane ring. The MP2 distance between H of HF and the thiirane sulfur was 2.164 A, in good agreement with the experimental distance, 2.193 A. 

Figure 2. Electrostatic potentials derived from 6-31G B3LYP-DFT//3-21G UHF calculations for Ubiquinone Qo in (a) the oxidized (Qox) and (b) the radical anion form (Qmd ) and lumiflavin in the oxidized (FIqx) and radical anion form (Fhad ). Contour lines are at 60 kcal moU intervals.

The mechanism of imidazole-2-ylidene-catalyzed transesterification has been studied using B3LYP DFT (Scheme 10). The reaction is predicted to involve neutral tetrahedral intermediates, TSl and ATSl, in which the catalyst imidazol-2-ylidene facilitates proton transfer from alcohol to the carbonyl oxygen by forming the tetrahedral intermediate TD <2005TL6265, 2005OL2453>. 

The RHF (Restricted Flartree-Fock) and B3LYP-DFT (Density Functional Theory) calculations were performed with 6-3IG basis sets using the Spartan. 02 Quantum Mechanics Program package. 

B3LYP DFT method, Becke 3-parameter hybrid exchange with the Lee-Yang-Parr correlation functional DFT density functional theory... 

Fig. 3 Electrostatic potential maps derived from B3LYP-DFT calculations for lumiflavin and ubiquinone in the respective oxidized (Fly and Qox) and radical anion forms (Flj-ad- and Qrad-)- Contour lines are at 60 kcal/mol intervals.

In our own experience, density functional calculations (B3LYP-DFT functional) are very well suited for a reliable prediction of vibrational spectra. TD (time dependent) calculations even give surprisingly good results for electronic transitions. 

Results of theoretical calculation at the B3LYP-DFT level using the 6-31 + G(d,p) basis set in ground and triplet states of stUbenes (c-1, t-1) and of 2,3-diphenylnor-bornene (2) were described [6]. Pronounced pyramidalization at the olefinic C atoms giving a PhCCPh dihedral angle of 51.0° in 32 was shown. 

Gas-phase DFT NMR calculations using the GIAO cluster approach for determining NMR shielding tensors, the hybrid B3LYP DFT functional and the... 

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