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Solvent Molecules Play a Role in an SNAr Reaction

preprint
submitted on 28.02.2019 and posted on 28.02.2019 by Yumiao Ma

Reaction between 4-nitrobenzonitrile and sodium methoxide (MeONa) exhibits unexpectedly low conversion and puzzling kinetics behavior, which is in sharp contrast to the prediction that reaction would be rapid and thorough made by density functional theory (DFT) calculations under implicit solvation. Free energy surfaces (FES) obtained by explicit solvation model including 62 solvent molecules differ greatly from those with implicit solvation. The real nucleophile is not methoxide anion but methanol-methoxide complex, and it is the entropy effect due to solvent molecules that modifies the FES. It is the first work revealing the significant modification of FES by explicit solvation for small molecule reactions.

History

Email Address of Submitting Author

mym15@mails.tsinghua.edu.cn

Institution

BSJ Institute

Country

China

ORCID For Submitting Author

0000-0002-0628-8864

Declaration of Conflict of Interest

No.

Version Notes

Noted on March 25th: The author received some comments that this phenomena is common and can be overcome by adding one or two solvent molecules into the model. It is NOT the case. The direct participation of solvent molecules and general acid/base catalysis is indeed very common, but in this case solvent molecules DO NOT directly participate in the reaction. They affect the shape of FES entropically, and only including large amount of explicit solvents could give correct results. This phenomena is different from the past solvent participated reactions.

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