Evaluation of J coupling constants from peak amplitudes of total correlation spectra

A novel method is presented for the evaluation of J values from total correlation spectra. The series expansion of the density matrix for a system undergoing isotropic mixing shows that a convenient approximation can be exploited to evaluate the extent of net transfer as a function of J values. Peak amplitude quantitation of short mixing time spectra provides tentative estimates of scalar couplings that can be further refined by fitting the experimental data with theoretical transfers obtained by full density-matrix calculation. The method is applied to conventional 2D TOCSY and heteronuclear resolved relayed TOCSY (SQCTOCSY) spectra of model compounds. The extracted coupling constants agree satisfactorily with the corresponding values obtained by 1D spectrum simulation.