Organic Chemistry

786 CHAPTER 18 Carbonyl Compounds II

70. When a cyclic ketone reacts with diazomethane, the next larger cyclic ketone is formed. This is called a ring expansion reaction.
    Provide a mechanism for this reaction.


71. The values of oxaloacetic acid are 2.22 and 3.98.

a. Which carboxyl group is more acidic?

b. The amount of hydrate present in an aqueous solution of oxaloacetic acid depends on the pH of the solution: 95% at

81% at 35% at 13% at 6% at and 6% at Explain this pH dependence.

72. The Horner–Emmons modificationis a variation of a Wittig reaction in which a phosphonate-stabilized carbanion in used instead
    of a phosphonium ylide.

The phosphonate-stabilized carbanion is prepared from an appropriate alkyl halide. This is called the Arbuzov reaction.

Because the Arbuzov reaction can be carried out with an ketone or an ester (in which case it is called a Perkow

reaction), it provides a way to synthesize -unsaturated ketones and esters.

a. Propose a mechanism for the Arbuzov reaction.

b. Propose a mechanism for the Horner–Emmons modification.

c. Show how the following compounds can be prepared from the given starting material:

1. CH 3 CH 2 CH

O

CHCCH 3

OCH 3

CH 3 CH 2 CH

O

2.

OO

(EtO) 3 P + Br CH 2 CR (EtO) 2 P CH 2 CR

+ CH 3 CH 2 Br

−

(EtO) 2 P CHCR

OOO Ostrong O

base

a,b

a-bromo a-bromo

(EtO) 3 PCH+ 3 CHCH 3

+ CH 3 CH 2 Br

Br

−

CH 3 CH P(OEt) 2

CH 3

O

CH 3 C P(OEt) 2

CH 3

strong O

base

++

−

O

CH 3 C P(OEt) 2

Et = CH 3 CH 2

CH 3

CH 3

CH 3

R

RR R

O

CC −O P(OEt) 2

O

C

pH=1.3, pH=3.1, pH=4.7, pH=6.7, pH=12.7.

pH=0,

OH

HO

O

O

O

oxaloacetic acid

pKa

+

− +

CH 2 Ν+N N 2

O O

cyclohexanone diazomethane cycloheptanone