Abstract
The tautomerism of 5-chlorobenzofuroxan, 5-bromobenzofuroxan, and 5-iodobenzofuroxan was studied by the proton magnetic resonance (PMR) at 60 MHz. The rate of intramolecular rearrangement between the tautomers was calculated from the PMR line shape, using the density matrix method of intramolecular nonmutual exchange. The activation parameters for the intramolecular rearrangement were found to be ⊿H≐̸=5∼24 kcal/mol, ⊿S≐̸=-34∼+33 cal/deg·mol. Structure of the transition state is discussed from electronic energies of the system and it was concluded that this reaction proceeds via a transition state of ψ-o-dinitrosobenzene produced by the electrocyclic ring opening reaction of benzofuroxan.
