A Guidebook to Mechanism in Organic Chemistry

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