Chemistry Reference
In-Depth Information
2
.
.
y
+
+
+
+
1
.
.
x
+
+
4
3
φ
1
_
+
+
+
_
_
_
+
φ
3
~
y
φ
2
~
x
_
_
+
+
_
+
φ
4
Figure 7.4 Coordinate system and H
uckel MOs for cyclobutadiene
€
With reference to the coordinate system of Figure 7.4, we first
choose c
4
¼
c
1
as additional arbitrary constraint. We then immedi-
ately obtain
1
2
ðx
1
x
2
x
3
þx
4
Þ/
x
f
2
¼ f
2x
¼
ð
7
:
80
Þ
a function having the same transformation properties as the
x-coordinate (left diagram in the second row of Figure 7.4). yz is a
nodal plane for this MO. Next, we choose c
4
¼
c
1
as additional
arbitrary constraint, therefore obtaining
1
2
ðx
1
þx
2
x
3
x
4
Þ/
y
f
3
¼ f
2y
¼
ð
7
:
81
Þ
a function having the same transformation properties as the y-co-
ordinate (right diagram in the second row of Figure 7.4). zx is now a
nodal plane for this MO.
f
2y
are the pair of HOMOs
belonging to the doubly degenerate energy level
f
2x
and
«
¼ «
;
which
2
3
