Organic Chemistry

830 CHAPTER 19 Carbonyl Compounds III

the resulting carboxylic acid has two more carbon atoms
than the alkyl halide. Similarly, methyl ketones can be pre-
pared by an acetoacetic ester synthesis; the carbonyl
group and the carbon atoms on either side of it come from
acetoacetic ester, and the rest of the methyl ketone comes
from the alkyl halide.

When planning the synthesis of a compound that re-

quires the formation of a new carbon–carbon bond, first

locate the new bond that must be made, and then determine

which of the atoms that form the bond should be the

nucleophile and which should be the electrophile.

Summary of Reactions

1. Halogenation of the of aldehydes and ketones (Section 19.4).


2. Halogenation of the of carboxylic acids: the Hell–Volhard–Zelinski reaction (Section 19.5).


3. The can serve as a nucleophile and react with an electrophile (Section 19.6).


4. The can serve as an electrophile and react with a nucleophile (Section 19.6).


5. Compounds with halogenated can form carbonyl compounds (Section 19.6).

base

O

RCH 2 CHCR′

O

RCH CHCR′

Br

a-carbons a,b-unsaturated

H

O

Br Nu

RCHCR

O

RCHCR

O

RCHCR

H 3 O+ Nu

Br 2

−

a-carbon

O

H

RCHCR

O

E

RCHCR

O

RCHCR−

base E+

a-carbon

1. PBr 3 (or P), Br 2


2. H 2 O

O

RCH 2 COH

O

RCHCOH

Br

a-carbon

O

RCH 2 CH X 2

H 3 O+

+

O

RCHCH HX

X

+

O

RCH 2 CR X 2

X 2 = Cl 2 , Br 2 , or I 2

HO−

excess

+ RC

X

X O

CR + 2X−

a-carbon