Key for Assignment of Point Groups 1 Is the molecule linear? Yes- Go to 2 No- Go to 3 2 Does it have a centre of inversion? Yes- Belongs to D∞h No- Belongs to C∞v 3 Does it have three or more different Cn axes with n > 2? Yes- Go to 4 No- Go to 5 4 Does it have a C5 axis? Yes- Belongs to I or Ih No- Belongs to T, Td, Th, O or Oh. 5 Does it have a rotational axis Cn with n > 1? Yes- Go to 8 No- Go to 6 6 Does it have a mirror plane? Yes- Belongs to Cs. No- Go to 7 7 Does it have a centre of inversion? Yes- Belongs to Ci. No- Belongs to C1. 8 Are there n C2 axes perpendicular to the principle axis, Cn? Yes- Go to 9 No- Go to 11 9 Is there a horizontal mirror plane? Yes- Belongs to Dnh. No- Go to 10 10 Are there n dihedral mirror planes? Yes- Belongs to Dnd. No- Belongs to Dn. 11 Is there a horizontal mirror plane? Yes- Belongs to Cnh. No- Go to 12 12 Are there n vertical mirror planes? Yes- Belongs to Cnv. No- Go to 13 13 Are there any S2n axes? Yes- Belongs to S2n. No- Belongs to Cn.