Lesson33 - Enolate and Enol Nucleophiles The enolate anion...

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The enolate anion is as an ________ nucleophile (two nucleophilic sites, carbon and oxygen). Electrophiles generally add to carbon rather than oxygen. The net result of a reaction at C-alpha is substitution (the electrophile, E+, replaces the carbonyl’s alpha hydrogen). Enolate and Enol Nucleophiles RCH C H O R HO RCH C O R RCH C O R E RCH C E O R ambident enolate anion α ± substituted product The enol is nucleophilic too Under basic conditions, the nucleophilic form will be the ____________ Under acidic conditions, the nucleophilic form will be the ____ enol enolate anion α -substituted product RCH C O R H E RCH C O R H E –H RCH C O R E enol tautomer
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Alkylation of Enolate Anions (Enolates are Ambident Nucleophiles) O + LDA O Li O Si(CH 3 ) 3 O CH 3 CH 3 I (CH 3 ) 3 Si Cl "O"-alkylation "C"-alkylation + LiCl + LiI These are [S N 2] reactions As the HOMO indicates, enolates are ambident nucleophiles, being reactive at both C α and oxygen. Consistent with the largest lobe of the HOMO being on C α , most electrophiles react at carbon; some very powerful electrophiles (and oxophilic electrophiles) react mainly at oxygen (e.g., silicon is strongly oxophilic). enolate HOMO
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Halogenation of the α -Carbon The Enol as a Nucleophile; Br 2 as an Electrophile Because the conditions are acidic, all intermediates are neutral or positively charged. The [A
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Lesson33 - Enolate and Enol Nucleophiles The enolate anion...

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