The covariance of the differences between experimental and theoretical chemical shifts as an aid for assigning two-dimensional heteronuclear correlation solid-state NMR spectra

A robust method for the assignment of two-dimensional heteronuclear correlations in the solid-state NMR spectra is described. It statistically evaluates the differences between measured and theoretical (obtained from first-principles calculations of the NMR chemical shielding property of periodic materials) chemical shifts. The values of the covariance of these differences, and of the standard deviations of the respective linear correlations, are elucidative for the spectral assignment process. The efficacy of the method is demonstrated for three crystalline systems: l-tyrosine hydrochloride, l-tyrosine ansolvate, and the polymorphic form I of o-acetylsalicylic acid.