2.6 All four of these molecules (and many more!) have the elements
E C2 σ σ`
In the same way all square planar molecules contain the elements
E C2 C 2 (=C24) 4C2 σ σ` I S4 , regardless of the chemical composition of the molecule e.g.
2.7 D6h The symmetry is similar to that of the square planar case, but the principal axis is a 6-fold axis not a 4-fold axis.
The symmetry symbol consists of three parts:
The number indicates the order of the principal (i.e. highest order) axis. This is conventionally taken to be vertical.
The small letter h indicates a horizontal plane.
The capital letter D indicates that there are n (=6 for benzene) C2 axes at right angles to the principal C n axis (C6 for benzene):