Kinetic isotope effect both results are large enough to be indicative of weakening of the C-N bond in the transition state that would occur in a concerted process. Since kinetic isotope effects arise from differences in isotopic masses, the largest observable kinetic isotope effects are associated with isotopic substitutions of hydrogen with deuterium (100% increase in mass) or tritium (200% increase in mass). Kinetic isotope effects from isotopic mass ratios can be as large as 36.4 using muons. They have produced the lightest hydrogen atom, H (0.113 amu), in which an electron orbits around a positive muon (μ) "nucleus" that has a mass
Kinetic isotope effect now relatively routine. Moreover, several qualitative and semi-quantitative models allow rough estimates of deuterium isotope effects to be made without calculations, often providing enough information to rationalize experimental data or even support or refute different mechanistic possibilities. Starting materials containing deuterium are often commercially available, making the synthesis of isotopically enriched starting materials relatively straightforward. Also, due to the large relative difference in the mass of deuterium and protium and the attendant differences in vibrational frequencies, the magnitude of the isotope effect is larger than any other pair of isotopes except protium and tritium, allowing both primary and secondary isotope