Abstract: Tetramethylpyrazine is labelled with tritium by microwave discharge activation (MDA)of tritium gas.The labelled sample is hydrogenated in the presence of 0.5%Pd catalyst on alumina-silica support, and the labelled sample is partially hydrogenated to form tetramethy ldihydropyrazine.Theoretical calculations(CNDO/2)show that the π-bond electron polar-zability (superdelocalizability) of the Pd-pyrazine ring is greater than those of the Pt-pyrazine ring, the Rh-pyrazihe ring or the pyrazine ring.