Investigating catalytic processes with parahydrogen:: Evolution of zero-quantum coherence in AA′X spin systems

A systematic outline for the elucidation of the nature of hydrogenation intermediates with a lifetime too short to be directly detectable with standard NMR methods is presented. The method takes advantage of the special nature of the parahydrogen density operator and its inherent enhancement factor. The key aspect of these experiments is the evolution of zero-quantum coherence which is contained in the parahydrogen density operator. Analytical coherence transfer functions have been derived which describe the evolution of this zero-quantum coherence in spin systems consisting of three spins 1/2 that form an AA'X spin system. The analytical expressions presented form a basis for a thorough investigation of crucial catalytic steps. (C) 1998 Academic Press.