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

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
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
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Strong, bulky, non-nucleophilic base such as LDA • Polar aprotic solvent • Low temperature (-78 ºC) Factors Favoring Thermodynamic Enolate • Strong base, but weaker than LDA (e.g. alkoxides) • Protic solvent (allows equilibration via reprotonation/deprotonation) • Room temperature (25 ºC) • Equilibration occurs faster at higher temp. Halogenation at the α-Carbon (23.7) • α-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...
View Full Document

This note was uploaded on 10/24/2011 for the course CHEMISTRY 623 taught by Professor Benson during the Spring '11 term at Kansas.

Page1 / 2

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

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online