**************** The 5th., Lab Seminar *****************

Date: Mon, June 13, 2005  PM 1:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Yusuke Ohta

Title: Direct Rate Measurements of the Reactions of Benzophenone 
with RMgX and RLi: Effects of Substituents and Reagent Connection on Rates
              M. Shimizu and H. Yamataka
              Bull. Chem. Soc. Jpn., 77 1751-1761 (2004)

Abstract:
 Rates of reactions of MeMgBr and MeLi with substituted benzophenones
(BPs) were determined by using a stopped-flow method. The Hammett plots
for the reactions of MeMgBr in THF and in Et2O at 0℃ gave ρ values of
0.99±0.09 and 0.99±0.08, respectively; such values were in excellent
agreement with the ρ value determined previously by competition experiments
in THF. The Hammett ρ value (0.40±0.07) for the reaction of MeLi in Et2O
at 0℃ also agreed with that determined by competition experiments within
experimental errors. A logarithmic plot of the rate constant vs the reagent
concentration for the reaction of BP and MeMgBr in THF gave a linear plot
with a slope of close to unity, whereas that in Et2O showed saturation at a
higher MeMgBr concentration, reflecting different aggregation states in
different solvents. An analogous plot for MeLi in Et2O gave a curved
logarithmic plot with a slope of 1/4 at a higher reagent concentration and a
slope of 1/2 at a lower reagent concentration range, suggesting that the
aggregation of MeLi is concentration dependent.

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