Addition of Anions
ADDITION OF ANIONS
As has already been seen (p. 130) the introduction of electron-with
drawing groups into an aromatic nucleus tends to inhibit electro
philic substitution and to make nucleophilic substitution possible.
The same is true of addition reactions: the introduction of F, N0 2 ,
CN, ^C=0, C0 2 Et, etc., on the carbon atoms of a double bond
causes the w electrons to become less available and attack by an anion
then becomes possible, though it would not have taken place with the
unmodified double bond:
PhCHiCH
O
s" Y I©©
o
0
s
R-MgBr <Sr \ I®©
C,H 4 Me-P —> Ph CH-CH^S-C.H. Me-p
R Oe
F F
c=c
F F
H®
o
s
Ph • CH—CH^1
2 - -S—CIt© ©
6 H 4 Me-/>
(^1) i
R
F **^F F
eoEt EtO>»C-
/
F
-C
ElOHV \
- EtO»-C- C-H
\
F F F
Some of the reactions have important synthetic applications,
(i) Cyanoethylation
Thecyano-group in acrylonitrile, CH^CH- CN, makes the /3-carbon
atom of the double bond respond readily to the attack of anions or
other powerful nucleophiles, the addition being completed by the
abstraction of a proton from the solvent:
ROCHjCHjCN
ROH.
CH, ,==CH^C^N
PhOCH,CH 2 CN
HSCH 2 CH 2 CN
RNH • CH 2 • CH 2 • CN