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Since the substrate octatriene is a "4n + 2" molecule, the Woodward–Hoffmann rules predict that the reaction happens in a disrotatory mechanism. Since thermal electrocyclic reactions occur in the HOMO, it is first necessary to draw the appropriate molecular orbitals. Next, the new carbon-carbon bond is formed by taking two of the p-orbitals ...
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs. [ 1 ] A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction.
In chemistry, Occam's razor is often an important heuristic when developing a model of a reaction mechanism. [ 47 ] [ 48 ] Although it is useful as a heuristic in developing models of reaction mechanisms, it has been shown to fail as a criterion for selecting among some selected published models. [ 6 ]
Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is different from chemical thermodynamics, which deals with the direction in which a reaction occurs but in itself tells nothing about its rate.
Figure 6:Reaction Coordinate Diagrams showing reactions with 0, 1 and 2 intermediates: The double-headed arrow shows the first, second and third step in each reaction coordinate diagram. In all three of these reactions the first step is the slow step because the activation energy from the reactants to the transition state is the highest.
Reactions can be either ring-opening or ring-closing (electrocyclization). Depending on the type of reaction (photochemical or thermal) and the number of pi electrons, the reaction can happen through either a conrotatory or disrotatory mechanism. The type of rotation determines whether the cis or trans isomer of the product will be formed.
4 electron electrocyclization reaction correlation diagram with a disrotatory mechanism. Evaluating the two mechanisms, the conrotatory mechanism is predicted to have a lower barrier because it transforms the electrons from ground-state orbitals of the reactants (Ψ 1 and Ψ 2) into ground-state orbitals of the product (σ and π).
Several drug candidates in this series have progress into clinical trials. The DA INV reaction was used to synthesise the PDE-I and PDE-II sections of (-)-CC-1065. The first reaction in the sequence is a DA INV reaction between the tetrazine and vinyl acetal, followed by a retro-Diels–Alder reaction to afford a 1,2-diazine product.