Schemes Generation of carbon nucleophiles by proton abstraction

The position of the equilibrium in these acid-base reactions wUl depend on the relative acidity of the carbon acid and of the species BH (or, conversely, the basic strengths of and the carbanion). Some approximate pK values for typical carbon acids and the conjugate acids of some species commonly employed as bases are shown in Table 1.1. The numerical values recorded are approximate, since there is no method of accurately establishing absolute acidity in a single solvent medium for 

CHAPTER 1 ALKYLATION OF CARBON VIA ENOLATES AND ENAMINES 0. 0 C2H5OCCH2COC2H5 + B OHO II 1 II C2H5OC-C-COC2H5 + BH 

From the pK values reported in Table 1.1, an approximate ordering of some substituents with respect to their ability to stabilize carbanions can be established. The order suggested is N02 C0R CN C02R S0R Ph R. 

By comparing the approximate pK values of the conjugate acids of the basic catalysts with those of the carbon acid of interest, it is possible to estimate the position of the acid-base equilibrium for a given reactant-base combination. If we consider the case of a simple alkyl ketone, for example, it can be seen that hydroxide ion, and primary alkoxide ions, will convert only a fraction of such a ketone to its anion  

The slightly more basic tertiary alkoxides are comparable to the enolates in basicity. 

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