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Alpha-substitution reactions occur at the position next to the carbonyl group, the α-position, and involve the substitution of an α hydrogen atom by an electrophile, E, through either an enol or enolate ion intermediate. ==Reaction mechanism== Because their double bonds are electron rich, enols behave as nucleophiles and react with electrophiles in much the same way that alkenes do. But because of resonance electron donation of a lonepair of electron s on the neighboring oxygen, enols are more electron- rich and correspondingly more reactive than alkenes. Notice in the following electrostatic potential map of ethenol (H2C=CHOH) how there is a substantial amount of electron density on the α carbon. Alpha substitution mechanism2 When an alkene reacts with an electrophile, such as HCl, initial addition of H+ gives an intermediate cation and subsequent reaction with Cl− yields an addition product. When an enol reacts with an electrophile, however, only the initial addition step is the same. Instead of reacting with CI− to give an addition product, the intermediate cation loses the OH− proton to give an α-substituted carbonyl compound.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbonyl alpha-substitution reactions」の詳細全文を読む スポンサード リンク
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