Step: 116

You saw the reference axis C₃ surely immediately. Colinear with it is S₆ (if you did not detect this axis, then you look up step 87 ; there this case was discussed in detail). Perpendicularly to C₃ three axes of proper rotation C₂ are available; when turn around these axles the upper CH₃ group is transferred in each case and turned around into the lower. Additionally three mirror planes s_d are present, which bisect the angles between C₂.
From occurring S₆ the existence of an inversion center (S₆³ = i follows, see step 91 ).
Note now all from these symmetry elements produced symmetry operations!

Go now to step 119 !