Electronic structure and decomposition reaction mechanism of cyclopropenone, phenylcylopropenone and their sulfur analogues: a theoretical study.

The electronic structure, the origin of the extraordinary stability and the reaction mechanisms of the decomposition reaction of the three-membered ring cyclopropenone (IO), its phenyl derivative (IIO) and its sulfur analogues (IS and IIS) have been investigated at the B3LYP/6-311+G** level of theory. All critical points on the reaction surface, reactants, transition states and intermediates were determined. Reaction rate constants and half-lives have been computed. Natural bond orbital (NBO) analysis has been used to investigate the type and extent of interaction in the studied species. Results indicate that the decomposition reaction occurs via a stepwise mechanism, with the formation of a short-lived intermediate. The characters of the intermediates for the decomposition of IIO and IIS are different. In case of IIO decomposition, the intermediate structure is of prevailing zwitterionic character, whereas that for the decomposition of IIS is of prevailing carbene character. Solvent effects are computed, analyzed and discussed.

Eclipsed acetaldehyde as a precursor for producing vinyl alcohol.

The MP2 and DFT/B3LYP methods at 6-311++G(d,p) and aug-cc-pdz basis sets have been used to probe the origin of relative stability preference for eclipsed acetaldehyde over its bisected counterpart. A relative energy stability range of 1.02 to 1.20 kcal/mol, in favor of the eclipsed conformer, was found and discussed. An NBO study at these chemistry levels complemented these findings and assigned the eclipsed acetaldehyde preference mainly to the vicinal antiperiplanar hyperconjugative interactions. The tautomeric interconversion between the more stable eclipsed acetaldehyde and vinyl alcohol has been achieved through a four-membered ring transition state (TS). The obtained barrier heights and relative stabilities of eclipsed acetaldehyde and the two conformers of vinyl alchol at these model chemistries have been estimated and discussed.

Toward the understanding of the metabolism of levodopa I. DFT investigation of the equilibrium geometries, acid-base properties and levodopa-water complexes.

Levodopa (LD) is used to increase dopamine level for treating Parkinson's disease. The major metabolism of LD to produce dopamine is decarboxylation. In order to understand the metabolism of LD; the electronic structure of levodopa was investigated at the Density Functional DFT/B3LYP level of theory using the 6-311+G** basis set, in the gas phase and in solution. LD is not planar, with the amino acid side chain acting as a free rotator around several single bonds. The potential energy surface is broad and flat. Full geometry optimization enabled locating and identifying the global minimum on this Potential energy surface (PES). All possible protonation/deprotonation forms of LD were examined and analyzed. Protonation/deprotonation is local in nature, i.e., is not transmitted through the molecular framework. The isogyric protonation/deprotonation reactions seem to involve two subsequent steps: First, deprotonation, then rearrangement to form H-bonded structures, which is the origin of the extra stability of the deprotonated forms. Natural bond orbital (NBO) analysis of LD and its deprotonated forms reveals detailed information of bonding characteristics and interactions across the molecular framework. The effect of deprotonation on the donor-acceptor interaction across the molecular framework and within the two subsystems has also been examined. Attempts to mimic the complex formation of LD with water have been performed.

Electronic structure of orotic acid III geometric feature and thermal properties of some transition metal orotic acid complexes.

The complexes of orotic acid with Co(II), Ni(II), Fe(III), Cu(II), and Cd(II) were prepared and their stoichiometry were determined by elemental analysis. Co(II) and Ni(II) give complexes with orotic acid of 1:1 ratio whereas that of the remaining transition metals give complexes of 1:2 ratio. The stereochemistry of the studied metal complexes has been established by analyses of their electronic spectra and magnetic susceptibilities. The mode of bonding in the studied series of metal complexes was established via, analysis of their infrared spectra. The present analysis leads to the conclusion that all metal ions studied coordinate to orotic acid via N(1) and the adjacent carboxylate group. Thermal decomposition studies of orotic acid complexes have been carried out as to understand the status of water molecules present in these complexes as well as to know their general decomposition pattern. Theoretical investigation of the electronic structure of the studied metal complexes has been carried out. MO computations at the HF-level were performed. Charge density distribution, extent of distortion from regular geometry, dipole moment, and orientation were computed and discussed.