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Endo/exo Selectivity (endo/exo + selectivity)

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Chemistry100%

Selected Abstracts

ChemInform Abstract: Regioselectivity and endo/exo Selectivity in the Cycloadditions of the Phthalazinium Dicyanomethanide 1,3-Dipole with Unsymmetrical Alkene and Alkyne Dipolarophiles.

CHEMINFORM, Issue 43 2001
DFT Theoretical Study., Unexpected Reversals of Regiochemistry: A Combined Experimental
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Oriented Electric Fields Accelerate Diels,Alder Reactions and Control the endo/exo Selectivity

CHEMPHYSCHEM, Issue 1 2010
Rinat Meir
Abstract Herein we demonstrate that an external electric field (EEF) acts as an accessory catalyst/inhibitor for Diels,Alder (DA) reactions. When the EEF is oriented along the "reaction axis" (the coordinate of approach of the reactants in the reaction path), the barrier of the DA reactions is lowered by a significant amount, equivalent to rate enhancements by 4,6 orders of magnitude. Simply flipping the EEF direction has the opposite effect, and the EEF acts as an inhibitor. Additionally, an EEF oriented perpendicular to the "reaction axis" in the direction of the individual molecule dipoles can change the endo/exo selectivity, favouring one or the other depending on the positive/negative directions of the EEF vis-à-vis the individual molecular dipole. At some critical value of the EEF along the "reaction axis", there is a crossover to a stepwise mechanism that involves a zwitterionic intermediate. The valence bond diagram model is used to comprehend these trends and to derive a selection rule for EEF effects on chemical reactions: an EEF aligned in the direction of the electron flow between the reactants will lower the reaction barrier. It is shown that the exo/endo control by the EEF is not associated with changes in secondary orbital interactions. [source]

Prediction of solvent effect on the reaction rate and endo/exo selectivity of a Diels,Alder reaction using molecular surface electrostatic potential

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2003
M. R. Gholami
Abstract Molecular surface electrostatic potential was used to predict the solvent effect on the reaction rate, endo/exo selectivity and diastereomeric excess of a Diels,Alder reaction. It is shown that these quantities can be expressed in terms of molecular surface electrostatic potentials of solvents which are obtained computationally by the HF/6,31++G* procedure. Regression analyses and an experimental database are used to obtain analytical representation of rate constant, endo/exo selectivity and diastereomeric excess. The models obtained show that the hydrogen bond donor ability of solvents on the above mentioned properties is substantial, whereas solvophobicity only affects the reaction rate and endo/exo selectivity of the reaction. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Oriented Electric Fields Accelerate Diels,Alder Reactions and Control the endo/exo Selectivity

CHEMPHYSCHEM, Issue 1 2010
Rinat Meir
Abstract Herein we demonstrate that an external electric field (EEF) acts as an accessory catalyst/inhibitor for Diels,Alder (DA) reactions. When the EEF is oriented along the "reaction axis" (the coordinate of approach of the reactants in the reaction path), the barrier of the DA reactions is lowered by a significant amount, equivalent to rate enhancements by 4,6 orders of magnitude. Simply flipping the EEF direction has the opposite effect, and the EEF acts as an inhibitor. Additionally, an EEF oriented perpendicular to the "reaction axis" in the direction of the individual molecule dipoles can change the endo/exo selectivity, favouring one or the other depending on the positive/negative directions of the EEF vis-à-vis the individual molecular dipole. At some critical value of the EEF along the "reaction axis", there is a crossover to a stepwise mechanism that involves a zwitterionic intermediate. The valence bond diagram model is used to comprehend these trends and to derive a selection rule for EEF effects on chemical reactions: an EEF aligned in the direction of the electron flow between the reactants will lower the reaction barrier. It is shown that the exo/endo control by the EEF is not associated with changes in secondary orbital interactions. [source]