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The influence of some steric and electron effects on the mechanism of aromatic nucleophilic substitution (S N Ar) reactions in nonpolar solvent
Author(s) -
Emokpae Thomas A.,
Atasie Nkechi V.
Publication year - 2005
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20109
Subject(s) - chemistry , steric effects , nucleophile , nitro , reaction rate constant , medicinal chemistry , nucleophilic substitution , aniline , solvent effects , benzene , reactivity (psychology) , substitution reaction , intermolecular force , kinetic energy , solvent , photochemistry , stereochemistry , catalysis , kinetics , organic chemistry , molecule , alkyl , physics , quantum mechanics , medicine , alternative medicine , pathology
Abstract Kinetic studies are reported for the reactions with aniline in benzene of a series of X‐phenyl 2,4,6‐trinitrophenyl ethers [X = H; 2‐, 3‐, 4‐CH 3 ; 2,4‐, or 2,6‐(CH 3 ) 2 ] a–f , and the results compared with those of the corresponding nitro derivatives. In the methyl series, kinetic data show that increasing substitution reduces drastically the rates of reactions indicative of the operation of some kind of steric effect. The unfavorable steric congestion at the reaction center appears to be unimportant in determining the kinetic order of the reactions. In general, the second‐order rate constants k A depend linearly on the square of nucleophile concentration. The change in the kinetic form observed in the nitro derivatives may be largely due to the electron‐withdrawing effect of the group. With the 2,6‐dinitro derivative, however, the uncatalyzed pathway k 2 takes all the reaction flux. Steric hindrance to intermolecular proton transfer from base to the ethereal oxygen of the intermediate is sufficient to make the base‐catalyzed pathway insignificant relative to the k 2 pathway. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 744–750, 2005