Remote secondary deuterium KIEs

Recently, Brown and co-workers (Nagorski et al., 1994 Slebocka-Tilk et al., 1995) have found large remote secondary deuterium KIEs in their extensive investigation of the electrophilic addition of bromine to 7-norbornylidene-7 -norbornane under a variety of conditions. 

A large inverse secondary deuterium KIE of 0.64 was observed in acetic acid at 25°C when the perdeutero (d2o) compound was the deuterated substrate. This large inverse deuterium KIE was attributed to the KIE for the rate-determining formation of the bromonium ion (62). Although a portion of this KIE is undoubtedly due to the inductive effect (deuterium is more electron-donating than hydrogen and the deuterated bromonium ion would 

The addition of bromide ion (Table 44) greatly retards the addition reaction in both methanol and acetic acid by making the kx step more reversible 

4Hie present authors (O.M. and K.W.) believe that the inductive KIE would be very much less than 0.71 because only the deuteriums close to the reaction centre would have a significant inductive contribution to the KIE. In fact, a secondary inductive KIE might be as small as a few per cent, i.e., kHlkD 0.96. 

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