Chemistry Reference
In-Depth Information
Taking the positive root, we have the following for the
p
energy of
butadiene:
<
3
2
K
1 Kekul
e
:
E
¼
Q
þ
ð
9
:
83
Þ
:
p
K
1 Kekul
e
þ
1 Dewar
:
E
¼
Q
þ
so that we obtain
D
E
¼
E
ð
K
þ
D
Þ
E
ð
K
Þ¼ð
1
:
73
1
:
5
Þ
K
¼
0
:
23K
<
0
ð
9
:
84
Þ
for the conjugation energy.
14
Calculation of the coefficients in butadiene proceeds through solution
of the system:
!
!
<
3
2
x
2
þ
3
2
x
þ
c
1
þ
c
2
þ
0
ð
9
:
85
Þ
:
c
1
þ
c
2
¼
1
p
3
2
3
x
c
2
¼
c
1
¼
0
:
for x
¼
1
:
ð
9
:
86
Þ
362c
1
73
3
2
2
Therefore, we obtain the following for the 'resonance' between Kekul
e
and Dewar structures in butadiene:
Y ¼
c
1
ðc
1
þ
0
:
362
c
2
Þ¼
0
:
94
c
1
þ
0
:
34
c
2
ð
9
:
87
Þ
giving
88
% c
1
;
12
% c
2
ð
9
:
88
Þ
which shows the greater importance of the Kekul
e structure versus the
Dewar structure.
15
14
Since the structures are different, it is appropriate to speak of conjugation and not of resonance
energy.
15
Always, Dewar structures, having long bonds, are sensibly less important than Kekul
e
structures, but their importance may increase with their number (e.g. naphthalene and
anthracene).
