Nucleophilic attack conjugate base mechanism

The second oxidation, which is normally slower than the first (which is why sulfoxides are so easily isolable), has the same mechanism in neutral or acid solution, but in basic solution it has been shown that the conjugate base of the peroxy compound (R 00 ) also attacks the SO group as a nucleophile " ... 

However, intramolecular nucleophilic participation by the conjugate base during protonolysis of a C—Hg bond is questionable. A study of the acidolysis of the carbon-mercury bond in unsymmetrical di-alkylmercurials rather suggests that the reaction proceeds via a three-center transition state.In any case, substantial kinetic and stereochemical evidence has led to the idea that reaction occurs by a concerted, front side attack with a transition state that involves a pentacoordinate carbon center. In some cases unimolecular mechanisms, SeI, also have been observed. 

Scheme 2.2. Proposed mechanism for the aromatisation of the 19-aldehyde intermediate via a hydroperoxy acetal, (a) Enolization step (b) enzyme-assisted nucleophilic attack by hydroperoxyl intermediate. AH A, acidic amino-acid residue and conjugate base. BjBH, basic amino-acid residue and...

The conjugate base of hydrogen cyanide is the cyanide ion ( C=Ns). Cyanide ion is a strong base and a strong nucleophile. It attacks ketones and aldehydes to give addition products called t anohydrins. The mechanism is a base-catalyzed nucleophilic addition attack by cyanide ion on the carbonyl group, followed by protonation of the intermediate. 

The catalytic cycle for stabilised or soft nucleophiles (which are the conjugate bases of acids whose pKi, is lower than 25) involves the direct attack of the nucleophile on the alkene coordinated to palladium. Part of the mechanism for substrate 11 is depicted in Scheme 8.5. 

The mechanism of the base-catalyzed addition to conjugated aldehydes and ketones is direct nucleophilic attack at the j3-carbon to give the enolate ion, which is subsequently protonated. 

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