Accurate coupling constants from two-dimensional correlation spectra by “J deconvolution”

Abstract

A practical procedure is described for the accurate determination of coupling constants from cross peaks in homonuclear correlation (COSY) spectra. It lends itself to computer automation and is applicable to cases where the splittings are not well resolved. In an extension of the method suggested by Bothner-By and Dadok ( J. Magn. Reson. 72, 540, 1987) the active splitting J a is deconvoluted by multiplication of the experimental time-domain signal S( t 2) by cosec( πJ ∗t ), where J ∗ is a trial coupling. The trick is to sample the cosecant function at appropriate symmetrically spaced intervals that avoid the singularities. Fourier transformation of S( t 2) Cosec ( πJ ∗t ) gives a “test spectrum” containing antiphase doublets, and the integral of its absolute magnitude goes through a pronounced minimum when J ∗ = J a . Accuracies of ±0.04 Flz can be achieved. Passive couplings can be measured by an analogous procedure. Once the couplings have been determined it is possible to reduce a two-dimensional cross peak to a singlet at the chemical-shift coordinates by deconvoluting the splittings one at a time.