DETERMINATION OF THE EXCHANGE INTEGRAL BY THE LOW-FIELD CIDNP IN INTRAMOLECULAR HYDROGEN ABSTRACTION REACTION OF POLYMETHYLENE-LINKED XANTHONE AND XANTHENE

The intramolecular hydrogen abstraction reaction in a series of polymethylene-linked xanthone and xanthene systems is investigated from the viewpoint of the magnetic field effect of the low-field chemically induced dynamic nuclear polarization (CIDNP) spectra. The magnetic field effect can be successfully simulated with the stochastic Liouville equation, and the effective exchange integral J between the two terminal radicals is determined from the peak of the magnetic field dependence. The effective J values thus determined are much larger than those obtained by the CIDEP method. The difference in the J values obtained by the CIDEP and CIDNP is discussed.