Negative charge, stabilization

Figure 16.18 Nucleophilic aromatic substitution on nitrochlorobenzenes. Only in the ortho and para intermediates is the negative charge stabilized by a resonance interaction with the nitro group, so only the ortho and para isomers undergo reaction.

A is correct. The carbonyl group withdraws negative charge, stabilizing the conjugate base of pyruvate,... 

Delocalization of the negative charge stabilizes the conjugate base... 

Wittig Alkenation Reactions. The tosyhnethylene phosphorane is classified as a stabilized Wittig reagent because of the extra negative charge stabilization by the sulfone substituent on the yUdic carbon. Other stabilized ylides include (methoxy-or ethoxycarbonylmethylene)triphenylphosphorane, cyano-... 

A qualitative comparison of acidity requires a comparison of the stabiUty of negative charges. The following discussion will develop a methodical approach for comparing negative charge stability. Specifically, there are four factors to consider (1) which atom is the charge on, (2) resonance, (3) induction, and (4) orbitals. 

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