Comparison of ΔG°\u3csub\u3eAcid\u3c/sub\u3e (gas phase) and kinetic acidities measured in methanolic sodium methoxide

Hydron exchange rates, k (M s ), using methanolic sodium methoxide were compared with ΔG° , (kcal mol ) (gas phase) for 9-phenylfluorene, C H CH(CF ) , m-CF C H CH(CF ) , p-CF C H CHClCF , m-CF C H CHClCF , 3,5-(CF ) C H CHClCF , fluorene and C F H. There is a good linear correlation for p-CF C H CHClCF , m-CF C H CHClCF and 3,5-(CF ) C H CHClCF , with the others falling off the line. The fluorinated benzyl compounds and pentafluorobenzene have near-unity isotope effects and therefore differ from the fluorenyl compounds. Although the acidity and the exchange rates for three of the compounds [9-phenylfluorene, C H CH(CF ) and p-CF C H CHClCF ] are similar, the important proton-transfer step to form a hydrogen-bonded carbanion intermediate and the subsequent breaking of that weak bond to form a free carbanion in methanol differ significantly for the fluoernyl compound compared with the two fluorinated benzylic compounds. © 1998 John Wiley & Sons, Ltd. exc Acid 6 5 3 2 3 6 4 3 2 3 6 4 3 3 6 4 3 3 2 6 3 3 6 5 3 6 2 3 3 6 4 3 3 2 6 3 3 6 5 3 2 3 6 4 3 -1 -1 -

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