Site selectivity kinetic isotope effect

A less well developed, but potentially less intrusive alternative is to block acidic sites with deuterium and to use the kinetic isotope effect to prevent lithiation If the substrate can be polylithiated, the use of dianions (with the last-formed anion being likely to be the most reactive) may give the required selectivity. 

Each of the two isomeric organolithiums 63 and 64 could be formed selectively by using deuterium to block lithiation at the other site via the kinetic isotope effect (see below).43 The less stabilised a-lithio species 63 have a tendency to undergo dearomatising cyclisations,44 45 as described in section 7.2.4.6. 

Selected entries from Methods in Enzymology [vol, page(s)] Add-base catalysis [with site-directed mutants, 249, 110-118 altered pH dependencies, 249, 110] commitment to [in determination of intrinsic isotope effects, 249, 343, 347-349 in interfacial catalysis, 249, 598-599 equilibrium isotope exchange in, 249, 443-479 hydrogen tunneling in, 249, 373-397] interfacial [competitive inhibitors, kinetic characterization, 249, 604-605 equilibrium parameters, 249, 587-594 forward commitment to, 249, 598-599 interpretation, 249, 578-586 (constraining variables for high processivity, 249, 582-586 kinetic variables at interface,... 

The Isotope Transient Kinetics (ITK) technique has been used to examine these thermally-induced and sulphur-induced ageing effects in mote detail, and specifically to assess whether the deactivation induced under a defined set of conditions is brought about as a result of a decrease in the number of active sites, or whether it is brought about by a decrease in the turnover frequency of the active sites. The CO-NO reaction was selected to probe these effects, since this reaction is known to be particularly sensitive to sulphur poisoning. 

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