predict IR spectra, dipole moments, the orbitals used in bonding,predict optical activity, interpret electronic spectra
used to described the symmetry of a molecule or ion even if no symmetry is present
The act of conducting the symmetry element
consists of no change. Every molecule has this element
which a 360o/n rotation results in a molecule indistinguishable from the original. This is also called an n-fold rotational axis and abbreviated Cn. A molecule can have more than one symmetry axis; the one with the highest n is called the principal axis, and by convention is assigned the z-axis
Plane of symmetry
is a plane of reflection through which an identical copy of the original molecule is given. This is also called a mirror plane and abbreviated ?. A symmetry plane parallel with the principal axis is dubbed vertical (?v) and one perpendicular to it horizontal (?h). A third type of symmetry plane exists: if a vertical symmetry plane additionally bisects the angle between two 2-fold rotation axes perpendicular to the principal axis, the plane is dubbed dihedral (?d).
Center of symmetry
or inversion center, abbreviated i. A molecule has a center of symmetry when, for any atom in the molecule, an identical atom exists diametrically opposite this center an equal distance from it. There may or may not be an atom at the center.
an axis around which a rotation by 360o/n, followed by a reflection in a plane perpendicular to it, leaves the molecule unchanged. Also called an n-fold improper rotation axis, it is abbreviated Sn, with n necessarily even.