Lecture 32 - Strong, bulky, non-nucleophilic base such as...

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1 Reading for Friday Chapter 23: 23.8-23.10 3 rd Exam Tomorrow April 14 th 6-7:30 PM 120 Budig Exam 3 will cover Chapters 20, 21 and 22 (all sections except those skipped) Chapter 23 Substitution Reactions of Carbonyl Compounds at the α Carbon Lithium Diisopropyl amide (LDA) A very strong, non-nucleophilic (i.e. bulky) base Enolates are Planar
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2 As a consequence, ketones with stereogenic center at α -C will racemize Enolates of Unsymmetrical Carbonyl Compounds (23.4) Kinetic enolate Less substituted enolate Formed faster due to lower steric hindrance during deprotonation Thermodynamic enolate More substituted enolate Lower in energy (alkyl groups stabilize enolates just like they do alkenes) Factors Favoring Kinetic Enolate
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Unformatted text preview: Strong, bulky, non-nucleophilic base such as LDA Polar aprotic solvent Low temperature (-78 C) Factors Favoring Thermodynamic Enolate Strong base, but weaker than LDA (e.g. alkoxides) Protic solvent (allows equilibration via reprotonation/deprotonation) Room temperature (25 C) Equilibration occurs faster at higher temp. Halogenation at the -Carbon (23.7) -H can be replaced by Cl, Br or I using Cl 2 , Br 2 or I 2 as reagent Acid-catalyzed reaction allows monohalogenation Base-catalyzed reaction difficult to stop after one halogenation The iodoform test for methyl ketones Formation of a yellow precipitate (CHI 3 ) is a positive result...
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Lecture 32 - Strong, bulky, non-nucleophilic base such as...

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