310-22 - Organic Lecture Series CH 310 N LECTURE 22...

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Organic Lecture Series 1 CH 310 N LECTURE 22 Textbook Assignment: Chap 19 Cont’d Homework (for credit): POW 7 posted (Due Mar 21) Today’s Topics: Aldol rxn-acidic & intramolecular; Claisen Notice & Announcements: Late start to OH today 2:30-2:45 Organic Lecture Series 2 Enolate Enolate Anions Anions and and Enamines Enamines Chapter 19
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Organic Lecture Series 3 • The most important reaction of enolate anions is nucleophilic addition to the carbonyl group of another molecule of the same or different compound – although these reactions may be catalyzed by either acid or base, base catalysis is more common The reaction results in a new C—C bond The The Aldol Aldol Reaction Reaction Organic Lecture Series 4 The product of an aldol reaction is –a β -hydroxyaldehyde or a β -hydroxyketone The The Aldol Aldol Reaction Reaction C O H(R') R C O H(R') R HC OH R C O H(R') R + H 3 O + OH - -hydroxycarbonyl C H R C O H(R') R -unsaturated carbonyl H 3 O + OH - Frequently, there is a second, dehydration step
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Organic Lecture Series •The product of an aldol reaction is –a β -hydroxyaldehyde –or a β -hydroxyketone CH 3 -C-H O 2 HO NaOH β 3 -CH-CH 2 -C-H OH O α + Acetaldehyde 3-Hydroxybutanal (a β -hydroxyaldehyde; racemic) O 3 -C-CH 3 2 -C-CH 3 O H Ba( OH ) 2 β α 3 3 -C-CH 2 -C-CH 3 O Acetone + 4-Hydroxy-4-methyl-2-pentanone (a β -hydroxyketone) The The Aldol Aldol Reaction Reaction Organic Lecture Series 6 Base-catalyzed aldol reaction Step 1: formation of a resonance-stabilized enolate anion Step 2: carbonyl addition gives a TCAI Step 3: proton transfer to O - completes the aldol reaction 2 =C-H O - 2 -C-H O H-O-H H-CH 2 -C-H O H-O - + An enolate anion + p K a 20 (w eak er acid) p K a 15.7 (stronger acid) 3 O 2 O 3 -CH-CH 2 O O - A tetrahedal carbonyl addition intermediate + The The Aldol Aldol Reaction Reaction
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Organic Lecture Series 7
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310-22 - Organic Lecture Series CH 310 N LECTURE 22...

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