31723-02-1Relevant academic research and scientific papers
Studies of the Transition-state Structure by the Method of Volumetric Steric Effects. Part 4. Transition State in Diels-Alder Reactions of (E)-1-Alkyl(alkoxy)buta-1,3-dienes with Alkyl Acrylates
El'yanov, Boris S.,Shakhova, Svetlana K.,Polkovnikov, Boris D.,Rar, Lev F.
, p. 11 - 16 (2007/10/02)
A method of studying transition-state structures by analysis of volumetric steric effects is proposed.The method is used to reveal features of the steric structure of the transition state in Diels-Alder reactions.The structure has been found to change from one approximating the structure of the prereactional complex to that resembling the half-chair adduct as the diene substituent changes from methyl to t-butyl.As this takes place, no intermediate half-boat adduct is formed.An increase in steric hindrance during the change in the substituent is regarded as the driving force responsible for the transition-state shift along the reaction co-ordinate.This is consistent with the Hammond postulate.The C=O and C=C groups of the dienophile in the endo-transition state are in the s-cis-conformation.
