ORGN 343 |
| A frequently invoked principle in organolithium chemistry is that lower aggregates are more reactive and that variation in aggregate concentrations is a major cause of the high sensitivity of organolithium rates and selectivities to solvation. The relative reactivity of multiple aggregates has rarely been quantified. We have built a RINMR system which allows us to study processes with an activation barrier as small as 8.25 kcal/mole at -135 deg C (t1/2=2.7 sec). We have used our system to study the relative reactivity of n-butyllithium dimer and tetramer towards a variety of common electrophiles. For the deprotonation of a variety of acetylenes, the rate of tetramer disappearance has been shown to be independent of acetylene concentration, indicating that the tetramer does not participate in the reaction. Using a combination of rapid-injection kinetics and competition studies we have estimated that the tetramer is at least 7 million times less reactive than the dimer.
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
1:00 PM-5:00 PM, Tuesday, 30 August 2005 Washington DC Convention Center -- 201, Oral
Division of Organic Chemistry |
