215F07-notes-9-28-07

215F07-notes-9-28-07 - Chem 215 F07 Notes Dr. Masato...

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Chem 215 F07 Notes – Dr. Masato Koreeda - Page 1 of 2. Date: September 28, 2007 Chapter 14 Aldehydes and Ketones: Addition Reactions at Electrophilic Carbons I-2. Reversible nucleophiles (cont’d) Type 4 nucleophiles: Trivalent nucleophiles Amines are sufficiently nucleophilic enough to add to ketone and aldehyde C=O carbons without activation of the C=O oxygen atom by an acid. However, the last dehydration step from the aminol intermediates requires an activation of the hydroxyl oxygen atom (by H+ or L.A.). (1) Imine formation [from a ketone/aldehyde and a 1°-amine] + O H H 2 N CH 3 N H CH 3 + H 2 O imine 1°-amine aldehyde ! or H + Mechanism: O H H 2 N CH 3 O H N CH 3 H H H B OH H N CH 3 H H B O H N CH 3 H H H B O H N CH 3 H H H aminol H N CH 3 H B N H CH 3 imine These two steps may be reversed in order. Those RR’C=N-Z formation reactions from RR’C=Os have the optimum rate at around pH = 4.7. If the conditions are too acidic, the formation of such derivatives becomes slow,
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215F07-notes-9-28-07 - Chem 215 F07 Notes Dr. Masato...

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