Organic Chemistry

This means that Grignard reagents and organolithium compounds cannot be prepared

from compounds that contain acidic groups

or groups). Because even trace amounts of moisture can destroy

an organometallic compound, it is important that all reagents be dry when organometallic

compounds are being synthesized and when they react with other reagents.

PROBLEM 30 SOLVED

Show, using any necessary reagents, how the following compounds could be prepared with

ethylene oxide as one of the reactants:

a. c.

b. d.

SOLUTION

a.

b.

c.

d. the same reaction sequence as in a, but with butyl bromide in the first step.

PROBLEM 31

Which of the following reactions will occur? (For the values necessary to do this

problem, see Appendix II.)

HOMgBr

There are many different organometallic compounds. As long as the metal is less

electronegative than carbon, the carbon bonded to the metal will be nucleophilic.

The reactivity of an organometallic compound toward an electrophile depends on

the polarity of the carbon–metal bond: The greater the polarity of the bond, the more

reactive the compound is as a nucleophile. The polarity of the bond depends on the

difference in electronegativity between the metal and carbon (Table 12.3). For

example, magnesium has an electronegativity of 1.2, compared with 2.5 for carbon.

This large difference in electronegativity makes the carbon–magnesium bond highly

δ−δ+

CMg

δ−δ+

CLi

δ−δ+

CCu

δ−δ+

CCd

δ−δ+

CSi

δ−δ+

CZn

δ−δ+

CAl

δ−δ+

CPb

δ−δ+

CHg

δ−δ+

CSn

CH 3 MgBr + HC‚CH ¡ CH 4 + HC‚CMgBr

CH 3 MgBr + CH 3 NH 2 ¡ CH 4 + CH 3 NMgBr

CH 3 MgBr + NH 3 ¡ CH 4 + H 2 NMgBr

CH 3 MgBr + CH 3 OH ¡ CH 4 + CH 3 OMgBr

CH 3 MgBr + H 2 O ¡ CH 4 +

pKa

Mg

Et 2 O

D 2 O

product of b CH 3 CH 2 CH 2 CH 2 MgBr CH 3 CH 2 CH 2 CH 2 D

PBr 3

product of a CH 3 CH 2 CH 2 CH 2 Br

Mg

Et 2 O H+

O

CH 3 CH 2 Br CH 3 CH 2 MgBr CH 3 CH 2 CH 2 CH 2 OH

1.

2.

CH 3 CH 2 CH 2 CH 2 Br CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 OH

CH 3 CH 2 CH 2 CH 2 OH CH 3 CH 2 CH 2 CH 2 D

¬C‚CH, ¬COOH

(¬OH, ¬NH 2 , ¬NHR, ¬SH,

Mg

THF

H 2 O

CH 3 CH 2 CHCH (^3) D 2 O
Br
D
CH 3 CH 2 CHCH 3
CH 3 CH 2 CHCH 3
CH 3 CH 2 CH 2 CH 3
MgBr
Section 12.11 Organometallic Compounds 469
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