rate law with rate constant kobs (equations (a)-(d)). For route @ where k, 2 k,, equation (a) applies. kobs = k, [aIkene] (a)For route @ with d[Z]/dt = 0, the observed rate constant is described by equation (b),which reduces to equation (c) or (d). kobs = k , , when k,[alkene] k _ (c) kobs = (k,k,/k-1) [alkene], when k, [alkene] < k _ (d) We followed the decrease in concentration of 1 a in benzene in the presence of excess NPM by analytical HPLC.[14. ''I The dependence of the kobs values obtained from the function In [l] = In [I],-kobs t (correlation coefficient r 2 0.999) on [NPM] at T = 303 K is plotted in Figure 1. Already at rela-I l o ' kobr I d T 0.0 2 :L O L 0.8 1.2 INPMI-Irnol.L-'l Fig. 1. k,,, =d[laj/dt as a function of [NPM]; see text. Conditions: T = 303 K, solvent benzene, [la] = 0.035 mol L-*, 2.5-to 39.9-fold excess of NPM. tively low excess of NPM a plateau is reached, that is the condition, k,[alkene] + k-of Eq. (c) is satisfied. Thus route 0, via the diazoalkene intermediate 2a, is confirmed by the kinetic study. From the temperature dependence of the limiting rate constant k , for T = 293-303 K, the following activation parameters were calculated: E, = 21.6 * 0.4 kcal mol-I, AH' = 21.0 0.4 kcal mol-', AS* = -3.4 1.2 cal K-' mol-'. In an analogous study with norbornadiene as trapping agent,['61 a plot of the dependence of rate on concentration of norbornadiene yields a line through the origin. This relationship is described by equations (a) and (d) and no distinction between routes @ and 0can be made.
