Theoretical and experimental reinvestigation of methoxide ion reaction with 7-methyl 4-nitro benzofuroxan

Abstract

DFT/B3LYP theoretical study has been performed in order to interpret the kinetic-thermodynamic competition between compounds obtained by reaction of the methoxide ion on the 7-methyl 4-nitro benzofuroxan. Geometry, atomic charge distribution, transition states, IRC path, thermodynamic, and kinetic parameters ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]*, [Formula: see text]*, and [Formula: see text]*) have been calculated for all possible products. In gaseous state or in the presence of water as solvent, all [Formula: see text] values were found to be negative, ranging from [Formula: see text]12.54[Formula: see text]kcal mol[Formula: see text] to [Formula: see text]29.85[Formula: see text]kcal mol[Formula: see text] in water, indicating that all possible products should form spontaneously. Those values indicated the possible observation of all products but experimenters only detect simultaneously two [Formula: see text]-complexes in C5 and C7 among three possibilities. The Fukui indices obtained by NBO atomic charge distribution confirm the super electrophilicity of those two sites. For transition states barriers, [Formula: see text]* ranged from 18.98[Formula: see text]kcal mol[Formula: see text] to 42.12[Formula: see text]kcal mol[Formula: see text] in gaseous state and from 18.59[Formula: see text]kcal mol[Formula: see text] to 24.22[Formula: see text]kcal mol[Formula: see text] in water. The unexpected result of our calculations is that the most stable compound is the unobserved carbanion but it also exhibits the highest activation barrier. Our results indicated the existence of two consecutive kinetic/thermodynamic competitions that occur in separate periods. The simultaneous observation of the three compounds is impossible because compound 4 occurs as a trace at the time compound 2 disappears completely. Experimental reinvestigation of the studied reaction leads by a very slow process to the earlier unobserved carbanion. Reaction mechanisms were also discussed on the basis of IRC calculations.