One- and two-dimensional exchange J-resolved CP-MAS NMR spectrum of adamantane

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Abstract
A combined technique of 1D and 2D exchange NMR and J-resolved CP-MAS NMR of dilute spins in solids and its application to study a spin exchange process of abundant spins in solids is described, and demonstrated for powdered adamantane. A high-resolution J-resolved NMR spectrum of a 13C nucleus obtained by applying homonuclear decoupling and magic angle sample spinning is employed to label the spin states of 1H spins bonded to the 13C nucleus. Perspective 2D exchange spectra are employed to map out connectivity between the proton spin states, and the rate constants for the 1H spin exchange involved are determined by 1D exchange NMR techniques. Discussions based on the total energy conservation enable us to conclude that the observed spin exchange processes are to be ascribed mainly to the flip–flop motion of 1H spins; the spin-lattice process is negligible. The rate constant for the flip–flop motion of the proton spins is determined to be (7±2)×103 s−1 at room temperature.