The rate of the fastest ene reaction between 4-phenyl-1,2,4-triazoline-3,5- dione (1) and 2,3-dimethyl-2-butene (2) is studied by means of stopped flow in solutions of benzene (k 2 = 55.6 ± 0.5 and 90.5 ± 1.3 L mol-1 s-1 ...