Chemistry 125: Lecture 70 April 19, 2010 Acyl Compounds (Ch. 18) -H Reactivity (Ch. 19) This For copyright notice see final page of this file

OH RC O Fischer Esterification (sec. 17.7a) H + H + + RO H + Tetrahedral Intermediate (A/D, not pentavalent transition state) substitution at C OR starts with addition

Victor Meyer 9/8/48 - 8/8/97 Geliebte Frau! Geliebte Kinder! Lebt wohl! Meine Nerven sind zerstört; ich kann nicht mehr. Victor Meyer ( ) introduced the idea of Steric Hindrance (1894) …the source of this behavior is stereochemical…the space filling of the neighboring groups vant Hoff (1874) Sachse (1891) Configuration Conformation

Tetrahedral Intermediate Fischer Esterification Didnt Work with 2,6-Dimethylbenzoic Acid STRAIN! Carboxylic Acid

Tetrahedral Intermediate (A/D) R Linear Acylium Intermediate (D/A, like S N 1) OH R C O substitution at C Fischer Esterification (sec. 20.8, p. 965) H + H + O + OR H + 100% H 2 SO 4 Pour into ROH Melvin Newmans Method (1941) (attaching second H + inhibits reversal) H+H+ + O H H H+H+ + sometimes

Acyl Derivatives from Ketene sec , p. 907 H 2 C=C=O Nu:

Remember PhCHO + O 2 Baeyer-Villiger Reaction (insert O) pp H - migration R - migration

Migration from Acyl Carbon L R X C O + R inserts X between R and C=O

Beckmann Rearrangement (insert N) pp inserts in anti bond

Beckmann Rearrangement (insert N) pp R - migration in cation

elongates acid by one carbon Arndt-Eistert Reaction (insert C) pp Wolff Rearrangement R - migration

Acidity Tables 19.1 (p. 933), 19.2 (p. 943), 19.3 (p. 958) pK a ~ 18 H

complete formation of enolate not just a little at equilibrium LDA hindered strong base (pK a = 36) (p. 944) pK a ~ 25 K ~ (slow attack on C=O, none on enolate)

Acid & Base H/D Exchange via enol and enolate (sec. 19.2a)

Racemization via enol and enolate (sec. 19.3)

-Halogenation ketones/aldehydes (19.4a) + Iodoform with base

-Halogenation carboxylic acids (19.4b) Hell-Volhard-Zelinsky

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