Theoretical Study of Intramolecular Proton Transfer Reactions in Some Thiooxalic Acid Derivatives

Selective one-pot synthesis of allenyl and alkynyl esters from beta-ketoesters

A convenient method is described for the dehydration of beta-ketoesters to generate conjugated and deconjugated alkynyl esters and conjugated allenyl esters. This sequential one-pot method involves the formation of a vinyl triflate monoanion intermediate that leads to the selective formation of alkynes or allenes depending on additives and conditions used. Product outcomes appear to be a function of unique mono- and dianion mechanisms which are described.

Theoretical study of a new group of corrosion inhibitors

In the present work, the molecular interactions of four amino acid compounds were simulated through the density functional theory (DFT) indexes to study their inhibitive properties. The prototype inhibitors previously synthesized 2-amino-N-decylacetamide (G), 2-amino-N-decylpropionamide (A), 2-amino-N-decyl-3-methylbutyramide (V), and 2-amino-N-decyl-3-(4-hydroxyphenyl)propionamide (T) were used to test the accuracy of this calculation. The generalized gradient approximation (GGA) was the ab initio approach used to optimize the ground state of the molecules. The simulation of molecular dynamics with force field (AMBER) was calculated to obtain the interaction energy between the metallic surface and the inhibitor molecules. A strong correlation of the global and local indexes with the inhibiting capacity was observed. The inhibitive properties of compounds on mild steel in an aqueous hydrochloric acid solution agreed well with those derived from the reactivity and selectivity indexes in gaseous phase.

Nature of Bonding in the Cyclization Reactions of (2-Ethynylphenyl)triazene and 2-Ethynylstyrene

The topological analysis of the electron localization function (ELF) has been applied to explore the nature of bonding in thermal cyclizations of (2-ethynylphenyl)triazene and 2-ethynylstyrene. These processes have been proposed to occur through both five- (i.e., coarctate) and six-membered (i.e., pericyclic) transition states. The analysis of electron delocalization, as measured from an irreducible ELF f-localization domain reduction diagram, allows us to characterize these cyclizations of 2-ethynylstyrene in terms of a more pronounced pericyclic or coarctate character than those associated with (2-ethynylphenyl)triazene. The latter evolve through pseudopericyclic and pseudocoarctate pathways. It is found that ELF results are also in good agreement with recent magnetic evidence data obtained from the anisotropy of induced current density (ACID) calculations.

A Theoretical Study on the Reaction Mechanism for the Bergman Cyclization from the Perspective of the Electron Localization Function and Catastrophe Theory

The reaction mechanism associated with the Bergman cyclization of the (Z)-hexa-1,5-diyne-3-ene to render p-benzyne has been analyzed by means of a combined use of the electron localization function (ELF) and the catastrophe theory on the basis of density functional theory (DFT) calculations (B3LYP/6-31G(d)). The complex electronic rearrangements of this reaction can be highlighted using this novel quantum mechanical perspective. Five domains of structural stability of the ELF occurring along the intrinsic reaction path as well as four catastrophes (fold-cusp-fold-cusp) responsible for the changes in the topology of the system have been identified. The multiple factors that occur along the intrinsic reaction coordinate path are presented and discussed in a consistent way. The topological analysis of ELF and catastrophe theory reveals that mechanical deformation of the C1-C2-C3 unit and closed-shell repulsion between terminal acetylene groups lead to an early formation of diradicaloid character at C2 and C5 atoms. Immediately after the transition structure (TS) is reached, the open-shell-singlet biradical becomes stable. Meanwhile, C1 and C6 atoms are preparing to be covalently bonded; that will finally occur at a distance of 1.791 A. In addition, a separation of the ELF into in-plane (sigma) and out-of-plane (pi) contributions allows us to discuss the aromaticity profiles; sigma-aromaticity appears in the vicinities of the TS, while pi-aromaticity takes place in the final stage of the reaction path, once the ring has been formed.

A comparative ab initio study of intramolecular proton transfer in model alpha-hydroxyalkoxides

A comparative ab initio study was performed on the intramolecular proton-transfer reaction that occurs in alpha-hydroxyethanoxy, alpha-hydroxyphenoxide, and alpha-hydroxyethenoxy anions. The intramolecular proton transfer occurs in a five-member atom arrangement, between two oxygen atoms separated by a carbon-carbon bond. The chosen systems serve as models for alpha-hydroxyalkoxide molecules where the carbon-carbon bond varies from a single bond (the glycolate anion or alpha-hydroxyethanoxide anion) to a part of an aromatic ring (the alpha-hydroxyphenoxide anion), and finally to a double bond (the alpha-hydroxyethenoxide anion). Particular attention was given to the evolution along the intrinsic reaction coordinate of such properties as energies, relevant structural parameters, Mulliken charges, dipole moments, and 1H-NMR chemical shifts to reveal the similarities and differences for the proton transfer in the model systems.