*Achary* Housecroft-9780131755536_04, 10/5/7, 23, 23:39, page: 97
Chapter 4 . Point groups
Fig. 4.10 Scheme for assigning point groups of molecules and molecular ions. Apart from the cases of n ¼ 1 or 1, n most
commonly has values of 2, 3, 4, 5 or 6.
Apply the strategy shown in Figure 4.10:
Are there three C2 axes
perpendicular to the
principal axis?
Is there a !h plane
(perpendicular to the
principal axis)?
Worked example 4.6 Point group assignments: 3
To what point group does POCl3 belong?
No
START
Is the molecule linear?
Does PF5 have Td , Oh or
Ih symmetry?
Is there a Cn axis?
No
Yes; a C3 axis containing the
P and two axial F atoms
Yes; each lies along an
equatorial P!F bond
Yes; it contains the P and
three equatorial F atoms.
STOP
The point group is D3h .
Self-study exercises
1. Show that BF3 belongs to the D3h point group.
2. Show that OF2 belongs to the C2v point group.
3. Show that BF2Br belongs to the C 2v point group.
The structure of POCl3 is:
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