Cycloaddition B3LYP functional

Table 13-3. Basis set dependence of activation (AEa) and reaction energies (AEr) computed using the B3LYP functional for the concerted gas-phase cycloaddition of ethylene to trans-butadiene [kcal/mol]. All calculations include zero-point vibrational contributions evaluated at the B3LYP/6-311+G(d,p) level.

Density functional theory methods using the hybrid B3LYP functionals have been performed to study geometries and energetics of several intramolecular [2+3] dipolar cycloadditions of azides to nitriles (Section 11.06.6.1) toward fused tetrazole formation, including tetrazoles 14 and 15 <2003JOC9076>. 

Analysis of 13C distribution in recovered alkynes using C4 atom as an internal standard led to experimental KIEs as collected in Table 4. For both catalysts significant isotope effect was observed for the terminal acetylenic carbon. Experimental KIEs are consistent with cyclopropenation via intact tetrabridged rhodium carbenoids and do so to support [2+2] cycloaddition. DFT calculations using B3LYP functional were complicated and did not give conclusive results. 

Ab initio Hartree-Fock and density functional theory (DFT) calculations were performed to study transition geometries in the intramolecular hetero-Diels-Alder cycloaddition reactions of azoalkenes 20 (LJ = CH2, NFI, O) (Equation 1). The order of the reactivities was predicted from frontier orbital energies. DFT calculations of the activation energies at the B3LYP level were in full agreement with the experimental results described in the literature <2001JST(535)165>. 

Density functional theory calculations (B3LYP/6-31G level) have provided an explanation for the stereodivergent outcome of the Staudinger reaction between acyl chlorides and imines to form 2-azetidinones (/3-lactams). When ketene is formed prior to cycloaddition, preferential or exclusive formation of ct5-j6-lactam (50) is predicted. If, however, the imine reacts directly with the acid chloride, the step that determines the stereochemical outcome is an intramolecular 5n2 displacement, and preferential or exclusive formation of trans isomer (51) is predicted. These predictions agree well with the experimental evidence regarding the stereochemical outcome for various reactants and reaction conditions. 

Individual activation energies from BP, BLYP, EDFl and B3LYP density functional models are similar (and different from those of Hartree-Fock and local density models). They are both smaller and larger than standard values, but typically deviate by only a few kcal/mol. The most conspicuous exception is for Diels-Alder cycloaddition of cyclopentadiene and ethylene. Density functional models show activation energies around 20 kcaPmol, consistent with the experimental estimate for the reaction but significantly larger than the 9 kcal/mol value obtained from MP2/6-311+G calculations. Overall, density functional models appear to provide an acceptable account of activation energies, and are recommended for use. Results from 6-3IG and 6-311+G basis sets are very similar, and it is difficult to justify use of the latter. 

The molecular geometries and the frontier orbital energies of heterophospholes 28-31 were obtained from density functional theory (DFT) calculations at the B3LYP/6-311- -G, level. The 1,3-dipolar cycloaddition reactivity of these heterophospholes in reactions with diazo compounds was evaluated from frontier molecular orbital (FMO) theory. Among the different types of heterophospholes considered, the 2-acyl-l,2,3-diazaphosphole 28, 377-1,2,3,4-triazaphosphole 30, and 1,3,4-thiazaphosphole 31 were predicted to have the highest dipolarophilic reactivities. These conclusions are in qualitative agreement with available experimental results <2003JP0504>. 

Density functional theory calculations using the hybrid functional B3LYP have been performed to study tetrazole formation by intramolecular [2+3] dipolar cycloaddition of organic azides and nitriles <03JOC9076>. 

In addition to isolation and characterization of the ruthenacycle complexes 18 or 32, the detailed reaction mechanism of the [2 + 2 + 2] cyclotrimerization of acetylene was analyzed by means of density functional calculations with the Becke s three-parameter hybrid density functional method (B3LYP) [25, 33]. As shown in Scheme 4.12, the acetylene cyclotrimerization is expected to proceed with formal insertion/reductive elimination mechanism. The acetylene insertion starts with the formal [2 + 2] cycloaddition of the ruthenacycle 35 and acetylene via 36 with almost no activation barrier, leading to the bicydic intermediate 37. The subsequent ring-... 

Density functional theory (DFT) calculations at the B3LYP/6-31H-G"" level were carried out on the 1,3-dipolar cycloadditions of various heterophospholes, including 1,3-azaphosphole, with diazo compounds across the P=N bond <2003JP0504>. In most cases, the dominant frontier orbital interaction is between HOMO(diazo) with LUMO(heterophosphole) however, 1,3-azaphosphole has a HOMO of high energy and for it, HOMO(heterophosphole)-LUMO(diazo) is also important (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital). 

Density functional theory (DFT) calculations (at the B3LYP/LANL2DZ level of theory) account completely for the regio-and stereochemical result of the silver-catalyzed azomethine ylides cycloaddition onto C70 (Fig. 34.6). A stepwise mechanism indicates that the origins of the observed selectivity are determined by the first step of the cycloaddition at the site, regio, and enantio levels. 

The 2 + 2/3 + 2-cycloaddition reactions of cyclic ketimines formed functionalized sultam-fused azetidines and dihydropyrroles in good yields and high enantio-selectivities. The Cu(I)/Lewis acid-catalysed 3+2/2+2-cycloaddition reaction of 0 sulfonyl azides (1) with terminal alkynes (2) yielded bis-/V-sulfonylcyclobutenes (3) that exhibit aggregation-induced emission enhancement in the solid state (Scheme 1). Density functional theory (DFT) at the B3LYP/6-311++G(d,p) level has been used to investigate the Mo(CO)6-catalysed intramolecular 2+2- or 2 + 2+ 1-cycloaddition reactions of 5-allenyl-l-ynes." ... 

---