CUMULATIVE deprotonation

As a general guide, lithiation by deprotonation using commercially available alkyllithiums is feasible if the new organolithium has at least three stars in the following cumulative scoring system ... 

Table II. Cumulative and Stepwise Stability and Deprotonation Constants for Cu(II)—Peptide Complexes0...

The strong destabilization of sp centers by fluorine is impressively demonstrated by the acidities of different fluorine-containing cyclopentadiene derivatives (Scheme 2.38) - despite the strong, cumulative negative inductive (—4) effect of five fluorine atoms, the acidity of pentafluorocyclopentadiene [90] is similar to that of cyclopentadiene. The reason for this unexpected behavior is that deprotonation would create one more fluorinated sp center. In contrast, the expected behavior is observed for the pentakis (trifluoromethyl) derivative, which is more acidic by 16 orders of magnitude [91]. 

Bott (1985) reported, however, an observation that strongly indicates the presence of the deprotonated form of the alkenediazonium salt 5.30. If this salt is kept with 0.05 equiv. OCDs K" for 20 h in the perdeuterated solvent mixture (CD3)2SO - CD3OD (5 2), almost complete exchange of the a-H for D is observed, but no nitrogen is evolved. It is likely that this exchange represents an acid-base equilibrium (5-7). The conjugate base 5.31 of this reaction is structurally related to the enol 5.25 with (at least) partial cumulative double bonds at the C(a)-atom ... 

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