ISSN:
1573-9171
Keywords:
Meisenheimer complexes
;
1,3,5-trinitrobenzene
;
2,4,6-trinitrotoluene
;
MNDO-PM3 method
;
reaction mechanism
;
solvation
;
proton transfer
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The semi-empirical quantum chemical MNDO-PM3 calculations of the enthalpies of formation of Meisenheimerortho- andipso-σ-complexes of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) with the phenoxide anion in the gas phase and in water are performed within the framework of the point dipole model. Based on the calculated heats and activation barriers to substitution of the nitro group by the phenoxyl group in TNB and TNT, the possibility of the reactions of TNB and TNT with the phenoxide anion in water is shown. These reactions in water occurvia the SNAr mechanism involving the correspondingipso-σ-complex as an intermediate. In the gas phase, the SNAr mechanism is impossible, because the reaction is strongly endothermic. In the case of TNT, the exothermic reaction of elimination of a proton from the methyl group by the phenoxide anion competes with nucleophilic substitution in a polar solvent. The activation energy calculated for this exothermic reaction is 8 kcal mol−1.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00698487
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