Kinetic results are reported for tritium exchange of several hydrocarbons related to fluorene with methanolic sodium methoxide. The second-order rate constant for fluorene increases with NaOMe concentration and a comparison with //_ results is presented. Primary isotope effects are high and indicate the absence of significant amounts of internal return, kH, kn, and ky are interrelated for 9-phenylfluorene and 9-methylfluorene. The secondary isotope effect for exchange of fluorene-9,9-d2 is 15%. Tritium exchange rates given as 104k2 (M-1 sec-1) at 45°, AH* (kcal/mol), and AS* (eu) are, respectively, l,12-o-phenylene-7,12-dihydropleiadene, 5630, 17.
Experimental primary isotope effects for LiCHA-catalyzed proton exchange are compared for toluene and triphenylmethane. For toluene at 25°, /cDexPti/A:TexPti = 2.82 in cyclohexylamine (CHA) and fcHexPti/kTexP« = 27.2 in cyclohexylamine-W/V-if (CHA-A). For triphenylmethane at 25°, kH,.,rjtl/7cTcxpii = 2.79 in CHA and &HexPti/&Te*Pti = 19.2 in CHA-,. Derived internal return values show that internal return is greater for triphenylmethane than for toluene. Mechanistic primary isotope effects for the proton transfer step are also derived. The resulting kiH/kiD value is about 11 for both hydrocarbons.Base-catalyzed hydrogen isotope exchange reactions are frequently complicated by internal return phenomena3•4 (eq 1). The primary hydrogen isotope(1) This work was supported in part by Grant No.
The reaction of the trichloromethyl radical with seven 1-substituted adamantanes was studied at 40°. The principle reaction observed was abstraction of bridgehead hydrogen atom. The relative rates of reaction have been correlated via use of the Taft equation. Correlation has also been possible using the Kirkwood-Westheimer model. the radical, exists.8 (8) P.
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