Theoretical investigation of methoxide ion reaction on the 7-methyl-4,6-dinitrobenzofuroxan

Abstract

Reaction of the methoxide ion on the 7-methyl 4,6-dinitrobenzofuroxan (DNBF) 1 has been studied theoretically by means of DFT/B3LYP technique in order to interpret the kineticthermodynamic competition between the three possible compounds that are carbanion DNBF -4 and two complexed forms (2, 3) of the methoxide group in positions 5 and 7 respectively. Optimized Geometry, nbo atomic charge distribution, thermodynamic/kinetic parameters (∆ r H°T, ∆ r S°T , ∆ r G°T, ∆H*, ∆S* and ∆G*) and IRC path have been calculated for possible products and their transitional states using water as solvent. All obtained ∆ r G°T are negative, ranging from -19.16 to -42.87 kcal mol -1 , indicating the possible observation of all products but the experimenters only detected the anionic form DNBF -. Fukui indices, which were calculated by means of NBO atomic charge distribution, confirm the electrophilicity of the sites C5 and C7. Transition states barriers, ΔG* are 14.97 , 15.16 and 21.94 kcal mol -1 for the three possible products 2, 3 and 4 respectively in water. As expected, the most stable compound is the carbanion but it exhibits also the highest activation barrier. If this situation engenders formally a double kinetic-thermodynamic competition, the very weak activation energy of the two complexes in C5 and C7 makes improbable the simultaneous detection of the three expected compounds.

Kinetic Studies on SNAr Reactions of Substituted Benzofurazan Derivatives: Quantification of the Electrophilic Reactivities and Effect of Amine Nature on Reaction Mechanism

“…The high thermodynamic stability of 6 is shown to derive from an especially high capacity of a para NO 2 group to stabilize a negative charge through resonance effects. It is to be noted that isomeric addition at substituted and unsubstituted ring positions has also been the subject of extensive experimental and theoretical studies .…”