Title

Comparing isotope effects and rates for the methanolic sodium methoxide reactions of 9-r-fluorene to those for p-CF3C6H4CHClR (R = CH2Cl, CH2F and CF3)

Document Type

Article

Publication Date

10-1-2002

Abstract

Kinetic primary isotope effects and activation parameters associated with the methanolic sodium methoxide-promoted dehydrohalogenation reactions of 9-(chloromethyl)fluorene and 9-(fluoromethyl)fluorene are reported and compared to for p-CF C H CHClCH Cl and p-CF C H CHClCH F. The element effect, k /k = 4 at 25 °C, for the fluorenyl compounds is only a tenth of the value, k /k = 54, obtained for the benzylic compounds. Also reported are the activation parameters for the methanolic sodium methoxide reactions of 9-(trifluoro)methylfluorene for deuterium exchange and dehydrofluorination, and are compared to those for p-CF C H CHClCF . In both cases the exchange reaction is faster than the elimination; however, in the fluorenyl system there is a large difference between the entropies of activation for exchange, ΔS = -14 eu, and elimination, ΔS = +10 eu; however, the ΔS of 12-13 eu are the same for the benzylic systems. The eliminations for 9-(chloromethyl)fluorene and 9-(fluoromethyl)fluorene are 80 to 1,000 times faster than those for p-CF C H CHClCH X. The reactions of 9-(trifluoromethyl)fluorene are favored over p-CF C H CHClCF by 200,000 for the dehydrofluorination and 1,000 for the exchange at 25 °C; however, due to the large differences in activation entropies, the exchange reaction is favored by 10 at -50 °C. 3 6 4 2 3 6 4 2 3 6 4 3 3 6 4 2 3 6 4 3 HCl HF HCl HF ≠ ≠ ≠ 7

Publication Name

Collection of Czechoslovak Chemical Communications

Volume Number

67

First Page

1505

Last Page

1516

Issue Number

10

DOI

10.1135/cccc20021505

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