2.7.2.1: Other Groups
- Page ID
- 294097
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D Groups
The D set of point groups are classified as Dnh, Dnd, or Dn, where n refers to the principal axis of rotation. Overall, the D groups are characterized by the presence of n C2 axes perpendicular to the principal Cn axis. Further classification of a molecule in the D groups depends on the presence of horizontal or vertical/dihedral mirror planes.
Group | Description | Example |
---|---|---|
Dnh | n perpendicular C2 axes, and a horizontal mirror plane (σh) | benzene, C6H6 is D6h |
Dnd | n perpendicular C2 axes, and a vertical mirror plane (σv) | propadiene, C3H4 is D2d |
Dn | n perpendicular C2 axes, no mirror planes | [Co(en)3]3+ is D3 |
C Groups
The C set of point groups are classified as Cnh, Cnv, or Cn, where n refers to the principal axis of rotation. The C set of groups are characterized by the absence of n C2 axes perpendicular to the principal Cn axis. Further classification of a molecule in the C groups depends on the presence of horizontal or vertical/dihedral mirror planes.
Group | Description | Example |
---|---|---|
Cnh | horizontal mirror plane (σh) perpendicular to the principal Cn axis | boric acid, H3BO3 is C3h |
Cnv | vertical mirror plane (σv) containing the principal Cn axis | ammonia, NH3 is C3v |
Cn | no mirror planes | P(C6H5)3 is C3 |
S Groups
The S set of point groups are classified as S2n, where n refers to the principal axis of rotation. The S set of groups are characterized by the absence of n C2 axes perpendicular to the principal Cn axis, as well as the absence of horizontal and vertical/dihedral mirror planes. However, there is an improper rotation (or a rotation-reflection) axis collinear with the principal Cn axis.
Group | Description | Example |
---|---|---|
S2n | improper rotation (or a rotation-reflection) axis collinear with the principal Cn axis | 12-crown-4 is S4 |