NMR-Investigations of Homogeneous Hydrogenation Reactions using Para Hydrogen
Homogeneous hydrogenations with ortho- or para-enriched hydrogen result in strongly enhanced 1H-NMR-polarization signals due to symmetry breaking during the reactions. Polarization is observed only, if the transferred atoms stem from the same molecule (“pair correlation”). The polarization pattern reflects the reaction path, e.g. the reaction of two different educts leading to the same product shows different polarization spectra.
Examples given include hydrogenation of certain alkines to alkenes as well as alkenes to alkanes using organometallic rhodium catalysts.