This thesis describes investigations utilising isotopic hydrogen gas (D2 and DT) and covering several areas of chemistry. The initial studies involved the selective alpha-labelling of pyridine and other N-heterocyclics via new hydrogen-deuterium exchange catalysts, identified via a parallel-chemistiy screening process. The new catalysts and associated methodology are applicable to labelling with tiitium as well as deuterium and are a significant improvement upon existing labelling approaches. The remaining studies involved the application of isotopes to studies of the hydrogenation of unsaturated hydrocarbons. initially the hydrogenation, and isotopic exchange reactions, of simple imbranched C5 alkenes and alkynes with D2 gas were examined. Although many aspects of the hydrogenation chemistry of pentenes and pentynes have been studied there is an interest in obtaining close to 100% selectivity in the reactions of these important industrial feedstocks. The studies were subsequently extended to the hydrogenation of the less-volatile phenyl-C3 unsaturated hydrocarbons, allowing studies with DT gas as well as D2. The work carried out in these two chapters includes a comparison of a novel l%Pd/Al2O3 catalyst developed by Johnson Matthey (JM)/Synetix with a standard catalyst 5% Pd/C catalyst routinely used for the hydrogenation of double bonds. Although these investigations are still in their initial stages, the results obtained suggest that the JM catalyst could prove more selective than the commonly used Pd/C. The above DT studies also enabled an investigation of the application of a new development in 3H-NMR spectroscopy, the 3H cryo-probe. This new technology was shown to provide a significant advance for the analysis of tritiated compounds and mixtures containing low levels of radioactivity. The last investigations concerned the facile exchange of isotope during the hydrogenation of terminal alkenes. This process was shown to be general and could well provide a novel methodology for the tritium labelling of this class of compounds.