text: Dichloromethane, . There is a  rotation axis which passes through the carbon atom and the midpoints between the two hydrogen atoms and the two chlorine atoms. Define the z axis as co-linear with the  axis, the  plane  as containing  and the   plane as containing . A  rotation operation permutes the two hydrogen atoms  and the two chlorine atoms. Reflection in the  plane permutes the hydrogen atoms while reflection in the  plane permutes the chlorine atoms. The four symmetry operations , ,  and   form the point group . Note that if any two operations are carried out in succession the result is the same as if a single operation of the group had been performed.
  Methane, . In addition to the proper rotations of order 2 and 3 there are three mutually perpendicular  axes which pass half-way between the C-H bonds and six mirror planes. Note that