Molecules are classified into based on their collection of symmetry elements. Low Symmetry: C1cap C sub 1 (no symmetry), Cscap C sub s (only a plane), Cicap C sub i (only inversion). High Symmetry: Tdcap T sub d (tetrahedral like CH4cap C cap H sub 4 Ohcap O sub h (octahedral like SF6cap S cap F sub 6 D∞hcap D sub infinity h end-sub (linear with inversion like CO2cap C cap O sub 2 Standard Groups: Cnvcap C sub n v end-sub Dnhcap D sub n h end-sub , etc., defined by the arrangement of axes and planes. 3. Character Tables
Only orbitals of the same symmetry can overlap to form bonds. This is the basis of SALCs (Symmetry Adapted Linear Combinations). Vibrational Spectroscopy: Symmetry & Group Theory in Chemistry
A vibration must change the molecule's dipole moment (matches in the character table). Molecules are classified into based on their collection
A is an action (like a rotation) that leaves the molecule looking exactly as it did before. Each operation is associated with a symmetry element (the point, line, or plane where the action happens). Identity ( ): Doing nothing. Every molecule has this. Rotation ( Cncap C sub n ): Rotating by around an axis. (e.g., C2cap C sub 2 180∘180 raised to the composed with power Reflection ( ): Reflecting through a plane. σvsigma sub v (vertical): Contains the main rotation axis. σhsigma sub h (horizontal): Perpendicular to the main axis. Inversion ( or plane where the action happens).