Spectral editing in (13)C MAS NMR under moderately fast spinning conditions.
Novel procedures for the spectral assignment of peaks in high-resolution solid-state (13)C NMR are discussed and demonstrated. These methods are based on the observation that at moderate and already widely available rates of magic-angle spinning (10--14 kHz MAS), CH and CH(2) moieties behave to a large extent as if they were effectively isolated from the surrounding proton reservoir. Dipolar-based analogs of editing techniques that are commonly used in liquid-state NMR such as APT and INEPT can then be derived, while avoiding the need for periods of homonuclear (1)H--(1)H multipulse decoupling. The resulting experiments end up being very simple, essentially tuning-free, and capable of establishing unambiguous distinctions among CH, CH(2), and --C--/-CH(3) carbon sites. The principles underlying such sequences were explored using both numerical calculations and experimental measurements, and once validated their editing applications were illustrated on a number of compounds.
Department of Chemistry (M/C 111), University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607-7061, USA.
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Frydman