Nucleophilic addition of hydroxide

Step 1 Nucleophilic addition of hydroxide ion to the carbonyl group ... 

The trihalomethyl ketone (RCCX3) so formed then undergoes nucleophilic addition of hydroxide ion to its carbonyl group triggering its dissociation... 

Base catalyzed nitrile hydrolysis involves nucleophilic addition of hydroxide ion to the polar C N bond to give an imine anion in a process similar to nucleophilic addition to a polar C=0 bond to give an alkoxide anion. Protonation then gives a hydroxy imine, which tautomerizes (Section 8.4) to an amide in a step similar to the tautomerization of an enol to a ketone. The mechanism is shown in Figure 20.4. 

Following formation of the amide intermediate, a second nucleophilic addition of hydroxide ion to the amide carbonyl group then yields a tetrahedral alkoxide ion, which expels amide ion, NHZ-, as leaving group and gives the car-boxylate ion, thereby driving the reaction toward products. Subsequent acidification in a separate step yields the carboxylic acid. We ll look at this process in more detail in Section 21.7. 

Treatment of red, ionic [Au(TPP)]Cl with aqueous sodium hydroxide in DMSO yielded a greenish brown product which was isolated by extraction with n-hexane. It was identified as a product of the nucleophilic addition of hydroxide to a meso (5-) position of the TPP ring, yielding a 5-hydroxy-5-H-porphyrin (hydroxyphlorin) derivative, Au(HOTPP) [303],... 

Another possible mechanism for the formation of 7-17 begins with nucleophilic addition of hydroxide to C-5 of 7-16. The resulting anion reacts with the epoxide ring, which opens to give 7-48. 

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