Elimination reactions, secondary /3-tritium

More experimental data where the secondary KIE was larger than the EIE were subsequently published by Subramanian and Saunders (1984). The 2-arylethyl system was employed in these studies because other relevant data, such as the primary deuterium KIE, were available for this reaction. Special techniques were developed to determine the primary and the secondary tritium KIEs for this system. Three isotopically distinct elimination reactions (49-51) are possible for a 2-arylethyl derivative tracer labelled with tritium at the 2-position. 

Table 36 Secondary /3-tritium KIEs for the E2 elimination reactions of PhCHTCH2—X at 50°C.a...

L is the hydrogen or deuterium atom that is not transferred in the elimination reaction and T is tritium that is present in tracer quantities. These substrates were chosen so that the reactions would have transition states ranging from very ElcB-like for [22], to central or intermediate for [23], to El-like for [24]. For practical reasons, the base/solvent system could not be kept constant as was originally intended. EtO /EtOH was used in the reaction with substrates [22] and [23] whereas Bu,0"/But0H was used with substrate [24]. Although the secondary tritium KIE (when L = H) for the reaction of [22] was... 

Lin, S., Saunders, W. H. (1994) Tunneling in elimination reactions -structural effects on the secondary beta-tritium isotope effect, J. Am. Chem. Soc. 116, 6107-6110. 

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