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)

Heinz F. Koch, William C. Pomerantz, Erik L. Ruggles, Martijn Van Laren, Anne Marie Van Roon

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2 Scopus citations

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-CF3C6H4CHClCH2Cl and p-CF3C6H4CHClCH2F. The element effect, kHCl/kHF = 4 at 25 °C, for the fluorenyl compounds is only a tenth of the value, kHCl/kHF = 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-CF3C6H4CHClCF3. 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-CF3C6H4CHClCH2X. The reactions of 9-(trifluoromethyl)fluorene are favored over p-CF3C6H4CHClCF3 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 107 at -50 °C.

Original languageEnglish (US)
Pages (from-to)1505-1516
Number of pages12
JournalCollection of Czechoslovak Chemical Communications
Volume67
Issue number10
DOIs
StatePublished - Oct 1 2002

Keywords

  • Activation parameters
  • Carbanions
  • Dehydrohalogenations
  • Fluorinated compounds
  • Isotope effects
  • Isotope exchange
  • Mechanism
  • Reaction kinetics

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