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MNDO Study of reaction pathways for S N 2 reactions. Menschutkin reaction potential energy surfaces
Author(s) -
Viers Jimmy W.,
Schug John C.,
Stovall Michael D.,
Seeman Jeffrey I.
Publication year - 1984
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540050614
Subject(s) - mndo , chemistry , pyridine , transition state , computational chemistry , ab initio , exothermic reaction , potential energy surface , reaction coordinate , molecular orbital , reaction mechanism , potential energy , medicinal chemistry , organic chemistry , molecule , catalysis , atomic physics , physics
MNDO molecular orbital calculations have been employed to investigate limited reaction pathways and potential energy surfaces for a series of S N 2 reactions. Model calculations for X − + CH 3 X ( X = H, F, OH, OCH 3 , and CN) indicate that the MNDO method gives qualitative agreement with ab initio studies except for the hydride–CH 4 exchange. Studies involving alkylation of pyridine (Menschutkin reaction) were also carried out. For the reaction of pyridine with CH 3 Cl, which involves charge separation, our MNDO studies (which do not include solvation effects) do not produce a characteristic S N 2 pathway. For the reaction of pyridine with trimethyloxonium cation [(CH 3 ) 3 O + ] as the alkylating agent, a well defined S N 2 reaction pathway was obtained; this reaction involves charge transfer. A potential energy surface for the pyridine–trimethyloxonium cation reaction shows the presence of a saddle point transition state that resembles starting materials, in agreement with the Hammond postulate for this exothermic reaction.