Crampton, M. R. and Emokpae, T. A. and Isanbor, C. and Batsanov, A. S. and Howard, J. A. K. and Mondal, R. (2006) 'Effects of ortho- and para-ring activation on the kinetics of SNAr reactions of 1-chloro-2-nitro and 1-phenoxy-2-nitrobenzenes with aliphatic amines in acetonitrile.', European journal of organic chemistry., 2006 (5). pp. 1222-1230.
Rate constants are reported for reaction of 4-substituted 1-chloro-2,6-dinitrobenzenes 1, 6-substituted 1-chloro-2,4-dinitrobenzenes 2, and some of the corresponding 1-phenoxy derivatives, 3 and 4, with n-butylamine, pyrrolidine and piperidine in acetonitrile as solvent. Values of k1, the rate constant for nucleophilic attack at the 1-position, increase with increasing ring-activation but may be reduced by steric repulsion at the reaction centre which increases in the order Cl < OPh, and n-butylamine < pyrrolidine piperidine. ortho-Substituents may also have adverse steric effects, and those of the trifluoromethyl group are particularly serious. X-ray crystal structures of phenyl 2,4-dinitro-6-trifluoromethylphenyl ether and phenyl 2,6-dinitro-4-trifluoromethylphenyl ether are reported. Base catalysis in the 1-phenoxy derivatives is attributed to rate-limiting proton transfer from the zwitterionic intermediates 6 to base. Values of rate constants for this process decrease with increasing steric congestion at the reaction centre and in the order n-butylamine > pyrrolidine > piperidine.
|Keywords:||Kinetics, Nucleophilic aromatic substitution, Steric hindrance, Substituent effects.|
|Full text:||Full text not available from this repository.|
|Publisher Web site:||http://dx.doi.org/10.1002/ejoc.200500774|
|Record Created:||26 Apr 2007|
|Last Modified:||08 Apr 2009 16:30|
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