Chemistry 125: Lecture 70April 19, 2010

Acyl Compounds(Ch. 18)

-H Reactivity(Ch. 19) This

For copyright notice see final page of this file

O HR C

O

Fischer Esterification (sec. 17.7a)

H +H+

+

ROH+

Tetrahedral Intermediate (A/D, not pentavalent transition state)

substitutionat C

OR

starts withaddition

Victor Meyer 9/8/48 - 8/8/97“Geliebte Frau! Geliebte Kinder! Lebt wohl! Meine Nerven sind zerstört; ich kann nicht mehr.”

Victor Meyer(1848 - 1897)

introduced the idea ofSteric

Hindrance(1894)

“…the source of this behavior is stereochemical…the space

filling of the neighboring groups”

van’t Hoff (1874)

Sachse (1891)

Configuration

Conformation

Tetrahedral Intermediate

Fischer Esterification Didn’t Workwith 2,6-Dimethylbenzoic Acid

STRAIN!

Carboxylic Acid

Tetrahedral Intermediate

(A/D)

R

Linear Acylium Intermediate

(D/A, like SN1)

O HR CO

substitutionat C

Fischer Esterification (sec. 20.8, p. 965)

H +H

+O+

ORH

+

100% H2SO4

Pour into ROH

Melvin Newman’s Method (1941)

(attaching second H+ inhibits reversal)

H++

O HH

H++

sometimes

Acyl Derivatives from Ketene sec. 18.11, p. 907

H2C=C=O

Nu:

Remember PhCHO + O2

Baeyer-Villiger Reaction (insert O) pp. 907-909

H- migration

R- migration

Migration from Acyl Carbon

LR

XC

O+

R

inserts X between

R and C=O

Beckmann Rearrangement (insert N)pp. 909-911

inserts in anti bond

Beckmann Rearrangement (insert N)pp. 909-911

R- migration in cation

elongates acid by one carbon

Arndt-Eistert Reaction (insert C) pp. 915-917

Wolff Rearrangement

R- migration

AcidityTables 19.1 (p. 933), 19.2 (p. 943), 19.3 (p. 958)

pKa ~ 18H

complete formation of enolatenot just a little at equilibrium

LDA hindered strong base (pKa = 36) (p. 944)

pKa ~ 25K ~ 1011

(slow attack on C=O, none on enolate)

Acid & Base H/D Exchangevia enol and enolate

(sec. 19.2a)

Racemization via enol and enolate(sec. 19.3)

-Halogenationketones/aldehydes (19.4a)

+

Iodoform with base

-Halogenationcarboxylic acids (19.4b)

Hell-Volhard-Zelinsky

End of Lecture 70April 19, 2010

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