MadSci Network: Chemistry

Re: nucleophiles, electrophiles, attack on carbonyls

Date: Sat Sep 13 17:34:50 2003
Posted By: Jerry Franzen, Professor, Chemistry
Area of science: Chemistry
ID: 1061852933.Ch

I would not agree with the perception that carbonyl groups are not attacked by electrohiles. Carbonyl groups are thought to be protonated by protons from acids as the first step in several mechanisms (e.g. esterification, acid hydrolysis of esters and amides); protons are certainly electrophiles. It is postulated that carbonyl groups are coordinated to Lewis acid electrophiles (such as AlCl3) in the Friedel-Crafts acylation reaction. It is true that many carbonyl reactions include the attack of a nucleophile, but a good number of these reactions are initiated by the attack of an electrophile, specially if the nucleophile is weak. In the presence of active electrophiles and weak nucleophiles, the carbonyl group is first attacked by an electrophile. In the presence of very active nucleophiles and the absence of active electrophiles, the carbonyl group is attacked by the nucleophile.

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