Abstract
Reactions of substituted benzylidene Meldrum’s acids and methylthiobenzylidene Meldrum’s acids with OH–, CF3CH2O– And HOCH2CH2S– in 50% DMSO-50% water. π-Donor effects, soft acid-base interactions and transition state imbalances
Highlights
We have focused mainly on reactions where the intermediate (2) accumulates to detectable levels[1,2,5,6,7,8,9,11,12,13] because this allows the determination of all individual rate constants
All kinetic experiments were performed in 50% DMSO–50% water (v/v) at 20 °C and conducted under pseudo–first–order conditions with the vinylic substrates as the minor component
One of the major motivations for this study was to learn more about potential transition state imbalances in the nucleophilic attachment steps
Summary
In a series of recent papers we have reported kinetic studies of nucleophilic vinylic substitution (SNV) reactions that proceed by the attachment–detachment mechanism (eq 1) typical for substrates activated by electron withdrawing groups (X, Y).[1,2,3,4,5,6,7,8,9,10,11,12,13] We have focused mainly on reactions where the intermediate (2) accumulates to detectable levels[1,2,5,6,7,8,9,11,12,13] because this allows the determination of all individual rate constants A major reason why 2 accumulates to detectable levels in these reactions is that the π– acceptor groups (X, Y) provide the necessary stabilization of the intermediate by delocalizing the negative charge This implies that the formation of 2 should show some of the characteristic features of reactions that lead to resonance stabilized anions in general. There is an accumulating database that confirms the expected correlation between intrinsic barriers and π–acceptor strength for these reactions but there is only a relatively small number of investigations that address the question of transition state imbalance. Information about the latter comes from the study of substituent effects that provide Brønsted–type structure–. Some of our data suggest the operation of the hard–soft acid–base principle.[24]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
