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Chapter 16-3 - CHEM 262 Wei You Chapter 16 Aldehydes and...

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1 CHEM 262 Wei You Chapter 16. Aldehydes and Ketones (3)
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2 Addition of Nitrogen Nucleophiles Ammonia, 1° aliphatic amines, and 1° aromatic amines react with the C=O group of aldehydes and ketones to give imines (Schiff bases) CH 3 CH H 2 N H + CH 3 CH=N H 2 O + + Acetaldehyde Aniline     An imine (a Schiff base) O An imine (a Schiff base) Ammonia Cyclohexanone + + NH 3 H 2 O O NH H +
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3 Addition of Nitrogen Nucleophiles Formation of an imine occurs in two steps Step 1: carbonyl addition followed by proton transfer Step 2: loss of H 2 O and proton transfer to solvent C O H 2 N-R H H C O: - N-R O H N-R H C + + O H H H H C O H N-R N-R H C O H H O H H C N-R O H H H   An imine + + + + + + H 2 O Note – imines are the prod of rxn of primary amines and C=O; enamines are prepared from rxn of secondary amines and C=O which we will see in Ch 19.
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4 Addition of Nitrogen Nucleophiles Secondary amines react with the C=O group of aldehydes and ketones to form enamines the mechanism of enamine formation involves formation of a tetrahedral carbonyl addition compound followed by its acid-catalyzed dehydration we discuss the chemistry of enamines in more detail in Chapter 19 O H-N H + N H 2 O An enamine Piperidine (a secondary amine) + + Cyclohexanone
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5 Addition of Nitrogen Nucleophiles a value of imines is that the carbon-nitrogen double bond can be reduced to a carbon- nitrogen single bond + Dicyclohexylamine Cyclohexanone (An imine) C yclohexylamine O N N H -H 2 O H 2 / Ni H + H 2 N A secondary amine
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6 Addition of Nitrogen Nucleophiles the carbonyl group of aldehydes and ketones reacts
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