SP56 Point group(part 1) #group theory #science #physicalchemistry #spectroscopy #symmetry #molecule

Ajouté : 2026-05-17

[00:00:00]Point group. First, are the low symmetry groups. C1 is the simplest point group and contains only the identity operation E. Molecules like CHBrClF belong to C1. Cs contains a single mirror plane sigma. Acetic acid is a representative example. Its only symmetry element is the molecular mirror plane. Ci contains an inversion center I. Here the substituted staggered ethane structure shown on the right is an example. It has no symmetry element other than inversion. Next, are the cyclic groups. Cn groups contain only the Cn axis. Hydrogen peroxide H2O2 is an example of C2 symmetry. Its structure looks like an open book. Cnv groups additionally contain a vertical mirror plane sigma v. As discussed earlier, a water H2O is C2v and ammonia NH3 is C3v.

[00:01:00]CnH groups contain a horizontal mirror plane sigma h. The trans dichloroethylene structure shown on the right belongs to C2h. It contains a molecular mirror plane and a C2 axis perpendicular to that plane.