CN0024 Photochemistry
Fall 2022
Symmetry & Group Theory II
Youn K. Kang • Sangmyung University
Point Groups
Molecules with the same symmetry elements are placed into point
groups. We can use a flow chart such as this one to determine the point
group of any object.
In our textbook and many other ones, there is similar type
of flow chart (Figure 4.7) that guides to the determination of
point group of any given molecule, but I personally prefers
one shown in the above slide which appears to be easiest
one I have ever found.
Major reason that I don’t like Figure 4.7 is that, according to
it, we have to determine the low symmetry group first,
which can be determined only after we try every possible
symmetry operation.
(Judging whether it is high symmetry group or not is not
that difficult if we are getting familiar with conventional such
systems.)
Thus you can take advantage of the flowchart in this slide.
However, understanding of all point groups in the textbook
is nonetheless important, thus will be described from now
on.
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
D¥h
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
C¥v
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
Ih
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3. [B12H12]2-
Ih
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
4. W(CO)6
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
4. W(CO)6
Oh
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
4.
5. B4Cl4
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
4.
5. B4Cl4
Td
Point Groups
Let’s practice with a number of examples.
1. O2, N2.
2. CO, NO+
3.
4.
5. CCl4, CH4, …etc
Td
Group of High Symmetry
Point Groups
Let’s practice with a number of examples.
6. CHBrClF
Td?
N
Point Groups
Let’s practice with a number of examples.
6. CHBrClF
C1
N
Point Groups
Let’s practice with a number of examples.
Then CHCl2F?
C1?
N
Point Groups
Let’s practice with a number of examples.
7. CH2Br2Cl2
N
Point Groups
Let’s practice with a number of examples.
7. CH2Br2Cl2
i
Ci
N
Point Groups
Let’s practice with a number of examples.
8. C2H2BrCl
N
Point Groups
Let’s practice with a number of examples.
9. C2H2BrCl
s
Cs
N
Point Groups
Let’s practice with a number of examples.
8. CHCl2F?
s
Cs
N
Groups of Low Symmetry