SN2 versus SN2′ Competition
The Journal of Organic Chemistry, vol. 87, pp. 8892–8901
Abstract
High Resolution Image Download MS PowerPoint Slide We have quantum chemically explored the competition between the S N 2 and S N 2′ pathways for X – + H 2 C═CHCH 2 Y (X, Y = F, Cl, Br, I) using a combined relativistic density functional theory and coupled-cluster theory approach. Bimolecular nucleophilic substitution reactions at allylic systems, i.e., C γ ═C β –C α –Y, bearing a leaving-group at the α-position, proceed either via a direct attack at the α-carbon (S N 2) or via an attack at the γ-carbon, involving a concerted allylic rearrangement (S N 2′), in both cases leading to the expulsion of the leaving-group. Herein, we provide a physically sound model to rationalize under which circumstances a nucleophile will follow either the aliphatic S N 2 or allylic S N 2′ pathway. Our activation strain analyses expose the underlying physical factors that steer the S N 2/S N 2′ competition and, again, demonstrate that the concepts of a reaction’s “characteristic distortivity” and “transition state acidity” provide explanations and design tools for understanding and predicting reactivity trends in organic synthesis.
Authors 4
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Affiliation as printed
Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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Affiliation as printed
Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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Radboud University Nijmegen · Vrije Universiteit Amsterdam
Affiliation as printed
Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Institute for Molecules and Materials (IMM), Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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Trevor A. Hamlin corresponding
Affiliation as printed
Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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