8．置換基の電子的性質−誘起効果と共鳴効果

8-1
Inductive Effect
δδδ
C
δδ
C
δ
C
δ−
X
C
C
C
X
X: Halogen, OH, OR, NR 2 , COR, NO 2 ....
(Li, B, Mg. Al etc.
δδ−
C
δ−
C
δ
BR 2
C
R
C
R
σ
Conjugated System delocalization of electrons
Conjugate System: πLone Pair
delocalization

π
a)
1,3-butadiene
Conjugated π Electron System
b) benzene
8-2
CH 2 CH CH CH 2
delocalization energy
pentadienes Heat of Hydrogenation
1,4-pentadiene
+ 2H 2
-254 kJ mol -1
-28 kJ mol -1
1,3-pentadiene
+ 2H 2
pentane
-226 kJ mol -1
benzene Heat of Hydrogenation
1,3,5-cyclohexatriene
cyclohexene
cyclohexane
+ 3H 2
+ H 2
-119 x 3 =
-357 kJ mol -1
-119 kJ mol -1
-151 kJ mol -1
+ 3H 2
benzene
-206 kJ mol -1
a) lone pair
H 2 C C
H
CH 2
δ
δ
H 2 C C
H
CH 2
allyl anion
b) p vacant p orbital
H 2 C C CH 2
H
allyl cation
δ
δ
H 2 C C
H
CH 2

8-3
8.3. Resonance
Canonical
Structureπ
Canonical
Structures
Resonance Hybrid
(a) 1,3-butadiene (i) (i)
CH 2 CH CH CH 2 CH 2 CH CH CH 2 CH2 CH CH CH 2
(ii)
(ii)
CH 2 CH CH CH 2
Formal Charge
Conjugate System: πLone Pair
σ
π

(6) CH 2
CH
8-4
(b) naphthalene
(c)
2-propenyl = allyl
δ
δ
CH 2 CH CH 2 CH 2 CH CH 2 CH 2 CH CH 2
δ
allyl cation
δ
CH 2 CH CH 2 CH 2 CH CH 2 CH 2 CH CH 2
allyl anion
(1)
CH 2
(2) +
(3) CH 2
C
CH 2 CH 2
(4)
(5)
CH 2
CH 2

8.4. Resonance EffectR
8-5
a) −R
δ+ δ−
CH 2 CH X Y CH 2 CH X Y
CH 2 CH X Y
δ+
δ+ δ−
CH 2 CH X Y
C C X Y
δ+
δ+ δ−
δ+ δ−
C C C C X Y C C C C X Y
C C C C X Y C C C C X Y
X=Y: NO 2 , COX, COR, SO 3 H, ......
π
π-Electron-withdrawing Groups
O
C
X
O
C
R
O
S
OH
nitrobenzene
O
O
N
O
O
N
O
2
O
N
O
δ−
O
O
N
O
O
N
O
O
N
O
δ+
δ+
δ+
N
δ+
δ−
O:

π
8-6
Unshared Electrons
CH 2 CH Z CH 2 CH Z
δ−
δ+
CH 2 CH Z
δ− δ+
π
C C C C Z C C C C Z
C C C C Z
Z: NR 2 , OR, Halogen
π Electron-donating Groups
aniline
H
H
H
H
N
N
N
N
H
H
H
H
H
δ− δ+
N
H
δ−
δ−
π
carbanions: C − amines
N N

Resonance Structures
1)
2)
3)
8-7
CH 2 CH 2
CH 2 CH 2 CH 2 CH 2
CH 2 CH CH CH 2
CH 2 CH CH CH 2 CH 2 CH CH CH 2
.....
.....
CH 2
O
CH 2
O
CH 2
O
CH 2 CH CH O
CH 2 CH CH O CH 2 CH CH O
O
N
O
2
O
N
O
O
N
O
.....
H
H
N
H
N
H
.....

8-8
(1)
CH 2 CH CH 2
(2)
CH 2
(3)
CH 3 O CH 2
(4)
CH
ClCH 2
CH CH 2
(5)
Cl
H
(6)
H 3 CO
Cl
H
(7)
O
C
H
Cl
H
(8)
CH 2
C
CH 3
O
(9)
N(CH 3 ) 2
(10)
H 3 C
C
H
C
C
OC 2 H 5
O
O
(11)
H 3 C
H
H
C
OH
(12)
H 2 C
CH 3
CH
C
O