Point Groups

1
Point Groups

• Chem 441 Inorganic Chemistry
• Dr. Jeff Seyler

2
Point Groups

• Set of symmetry operations that describes a
  molecules overall symmetry
• Summarized in character tables (later notes)
• Identified by a special label
• C1, Cs, C?v, D?v, Td, Oh, Cnv, Cnh, Dnv, Dnh
• Can be assigned by following a flow chart
• series of yes/no questions

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Flow Chart

• Concept from Dragos Physical Methods in
  Inorganic Chemistry text

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Conventions

• The x, y, z coordinate system places the xz plane
  on the paper, the z axis is vertical
• The principle axis is defined as the highest n
  rotation axis, i.e. C3 for NH3
• The z-axis is assigned as the principle rotation
  axis

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Examples

• Special groups
• CO2, D?v
• HCN, C?v
• Td, CH4
• Oh, PF6-1
• Low symmetry
• C1, CBrClFI
• Ci, anti conformer of R,S-1,2-dichloro-1,2-difluor
  oethane
• Cs, ClNO
• Cn, Cnh, and Cnv groups
• Dn, Dnh, and Dnv groups (n C2s perpendicular to
  Cn)

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Examples
C3v C3 axis ? to page
D2h three ? C2 axes
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Examples
C2v
D4h
8
Examples
propeller molecules C3 or D3
Replace N w/ C gives D3
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Examples
C1
In solution, may act like C2, depending on
orientation of the Cp ligands.
10
Examples
Ci
11
Examples
J. Am. Chem. Soc. 127(2005), 2382
12
Examples
Organometallics, 23 (2004), 946
13
Examples
C2
Organometallics, 23 (2004), 946