Equivalence Between Synthetic Decoupling and 2-Field Autocorrelation NMR Spectroscopy

It is shown that the recently introduced synthetic decoupling method, which correlates two lists of single-transition NMR frequencies acquired at two different fields to construct in silico a pure-shift spectrum, is equivalent to an experiment where free evolution periods at these two fields are autocorrelated in a 2D fashion. Numerical simulations are utilized to investigate these hypothetical 2-field 2D experiments that yield isotropic chemical-shift information by refocusing either scalar or quadrupolar couplings, in solution and solid state, respectively. In this latter case, both static and magic-angle spinning conditions are considered. It is shown that projections of the 2D data set taken at angles amounting to arctan(1) and arctan(1/), where = B0high/B0low, for scalar and quadrupolar couplings, respectively, are isotropic and can be scaled to directly yield the pure chemical shifts. For such purpose, a scaling factor is introduced. In the case of quadrupolar spins, the obtained pure-shift projections are also free from the isotropic part of the second-order quadrupolar broadening. The spectral resolution achieved by different relative strengths of the two external fields is considered.