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Quantum Chemical Characterization of Factors Affecting the Neutral and Radical-Cation Newman-Kwart Reactions

preprint
submitted on 16.12.2018 and posted on 17.12.2018 by Sina Chiniforoush, Christopher J. Cramer
Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol–1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol–1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality.

Funding

U.S. DOE, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences (Award DE-FG02-17ER16362).

History

Email Address of Submitting Author

chini006@umn.edu

Institution

University of Minnesota

Country

US

ORCID For Submitting Author

0000-0002-8428-4228

Declaration of Conflict of Interest

no conflicts of interest

Exports