. dedicate this work to the memory of late Prof. A. Schweiger.
AbstractUsing a DFT based Ligand Field treatment (LFDFT) of the electronic structure of Co(II) and Cu(II) porphyrins (CoP and CuP) we analyse the origin of their EPR spectra. From a comparison between theoretical result on Co model clusters (CoP and CoP-ZnP dimer) we conclude that the g-tensor values are very sensitive to the axial coordination which stabilizes a 2 A 1 ground state in good agreement with experimental data. In contrast, DFT overestimates Cu-ligand covalency, leading to large discrepancy with experiments, and hence the orbital contribution to the computed g-values is too small. Using a numerical adjustment of nuclear charge for Cu, a good agreement between the computed and the experimental g-tensor values is observed. The influence of the DFT functional on the calculated g-tensor is also discussed.
The Diels–Alder
reaction (DA) between various mono- and
disubstituted 1,3-butadiene (Dn-1 to Dn-10) and 2-bromocyclobutenone (DPh) was carried out in
gas phase using density functional theory (DFT) at the M06-2X/6-31+g**
level. The reaction was found to proceed through a concerted asynchronous
transition state. Further, the asynchronous and early nature of the
transition state was clearly pinpointed with the frontier molecular
orbital (FMO) and bond order index (BOI) analyses. The intermolecular
hydrogen bonding interaction along with steric encumbrance in the
transition state were found to be the predominant factors in controlling
the reactivity of the dienes. Among the investigated dienes, Dn-6 was found to be the most reactive diene which is attributed
to its low activation barrier due to the presence of strong intermolecular
H-bonding interactions. These factors were further supported by quantum
mechanical calculations using global descriptor indexes, natural bond
orbital analysis, and quantum theory of atoms in molecules analysis.
These theoretical results were found to be in good agreement with
the previous experimental findings.
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