Collect. Czech. Chem. Commun. 2002, 67, 1505-1516

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 and Anne-Marie van Roon

Department of Chemistry, Ithaca College, Ithaca, NY 14850, U.S.A.


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4. Ref.3b, p. 5098, gives the equation for calculating aT. The exponent used for the Swain–Schaad relationship is 2.344 instead of the original 2.26.
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10. Koch H. F., Lodder G., Koch J. G., Bogdan D. J., Brown G. H., Carlson C. A., Dean A. B., Hage R., Han P., Hopman J. C. P., James L. A., Knape P. M., Roos E. C., Sardina M. L., Sawyer R. A., Scott B. O., Testa C. A., III, Wickham S. D.: J. Am. Chem. Soc. 1997, 118, 9965. <>
11a. Melander L: Isotope Effects on Reaction Rates, p. 24. Ronald Press, New York 1960.
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12. Koch H. F., Dahlberg D. B.: J. Am. Chem. Soc. 1980, 102, 6102. For an example, see Fig. 1, case d, on p. 6103. <>
13. We use 3.344 for the Swain–Schaad exponent as recommended in ref.3b.
14. For a discussion of this, see ref.10, p. 9967.
15. Calculations using B3LYP/6-31+G(d,p) on the reactions of C6H5CHClCF3 and methoxide ion with two methanol molecules of solvation result in the encounter complex 7.8 kcal mol–1 more stable than the hydrogen-bonded carbanion. To form the free carbanion and (HOCH3)3 requires another 7.3 kcal mol–1. Koch H. F., DeTuri V. F.: Unpublished results.
16. The methanolic sodium methoxide protodetritiation of 9-(trifluoromethyl)fluorene-9-t was reported in ref.8 between –45 and –31 °C. The temperature dependence plot has sufficient error not to allow extrapolation to –75 °C. The kD/kT = 2.44 at –50 °C, which would have the Swain–Schaad relationship predict a kH/kD value of 8.1 at –50 °C and should be even larger at –75 °C.
17. Koch H. F., Tumas W., Knoll R.: J. Am. Chem. Soc. 1981, 103, 5423. <>
18. Koch H. F. in: Fundamentals of Carbanion Chemistry (E. Buncel and T. Durst, Eds). Elsevier, Amsterdam 1988. This is discussed for the reactions of C6H5CHBrCFClBr, pp. 333–335.
19. More O’Ferrall R. A., Warren P. J.: J. Chem. Soc., Chem. Commun. 1975, 483. <>
20. The rate constant reported in ref.19 for 9-(chloromethyl)fluorene is within 2% of the one we extrapolate from our kinetics carried out between –45 and 0 °C.
21. The Arrhenius parameters for 9-(chloromethyl)fluorene are normal with AH/AD = 1.0 and the magnitude of the isotope effect coming from __MATH__ = 1.1 kcal mol–1. On the other hand, the values for 9-(fluoromethyl)fluorene are AH/AD ≈ 4 and __MATH__ ≈ 0.4. This results in the loss of HF having a larger isotope effect than the loss of HCl at 25 °C and a smaller one at –50 °C. Both compounds have experimntal rate constants at 0 °C.