318-13 - Organic Lecture Series CH 318 N LECTURE 13...

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Organic Lecture Series 1 CH 318 N LECTURE 13 Textbook Assignment: Chapter 16 Homework (for credit): POW 6 posted Today’s Topics: Aldehydes/Ketones-reactions Notice & Announcements: Exam 1: Hard copies in Chem Office Organic Lecture Series 2 Aldehydes Aldehydes And And Ketones Ketones
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Organic Lecture Series 3 Addition of Nitrogen Addition of Nitrogen Nucleophiles Nucleophiles • Secondary amines react with the C=O group of aldehydes and ketones to form enamines enamines (alk (alk en en e and and amine amine ) – the mechanism of enamine formation involves formation of a tetrahedral carbonyl addition compound followed by its acid-catalyzed dehydration OH - N H + NH 2 O An enamine Piperidine (a secondary amine) + + Cyclohexanone Organic Lecture Series 4 N O HO N H H O H Protonated Ketone H N-Protonated Amino-alcohol N H
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Organic Lecture Series 5 HO N H Amino-alcohol N H O-Protonated N H 2 o Carbocation H N Enamine Product H H Organic Lecture Series 6 Addition of Nitrogen Nucleophiles Addition of Nitrogen Nucleophiles – the carbonyl group of aldehydes and ketones reacts with hydrazine and its derivatives in a manner similar to its reactions with 1° amines OH 2 NNH 2 NNH 2 H 2 O + Hydrazine + A hydrazone H 2 N -NHCNH 2 H 2 N -OH H 2 N -NH H 2 N NO 2 O 2 N Reagent, H 2 N-R Hydroxylamine Oxime Phenylhydrazine 2,4-Dinitrophenyl- hydrazine Semicarbazide 2,4-Dinitrophenylhydrazone Semicarbazone Name of Derivative Formed Name of Reagent Phenylhydrazone O
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Organic Lecture Series 7 Acidity of Acidity of α -Hydrogens Hydrogens Hydrogens alpha to a carbonyl group are more acidic than hydrogens of other hydrocarbons (e.g. alkanes, alkenes, aromatic). Acidity is measured as K a O H H H H α α Organic Lecture Series 8 HA + H 2 O H 3 O + A - [H 3 O + ] [A - ] [HA] [H 2 O] K eq = 3 O + - ] [HA] 2 O] K = 3 O + - ] K a = Freshman Flashback!! Note: l and s are not used in K
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Organic Lecture Series 9 Acidity of Acidity of α -Hydrogens Hydrogens Hydrogens alpha to a carbonyl group are more acidic than hydrogens of alkanes, alkenes, and alkynes but less acidic than the hydroxyl hydrogen of alcohols CH 3 2 O- H O 3 CCH 2 - H 2 =CH- H 3 2 - H 3 CC - H Type of Bond pK a 16 20 25 44 51 pKa = -log Ka Organic Lecture Series 10 α -Hydrogens are more acidic because the enolate anion is stabilized by: 1. delocalization of its negative charge 2. the electron-withdrawing inductive effect of the adjacent electronegative oxygen 3 -C-CH 2 - H O :A - O 3 -C CH 2 O - 3 -C=CH 2 H-A Resonance-stabilized enolate anion + + Note: α -hydrogens are not so acidic that they will destroy organometallic reagents
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Organic Lecture Series 11 Keto Keto -Enol Tautomerism Enol Tautomerism
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This note was uploaded on 03/23/2010 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas.

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318-13 - Organic Lecture Series CH 318 N LECTURE 13...

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