Enantiomorphic Point Groups

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Definition

The point groups that possess no improper rotations are called enantiomorphic. Enantiomorphic molecules have right-handed and left-handed forms, although in nature usually one form strongly predominates over the other. Most biologically important molecules are enantiomorphic, e.g. amino acids (L form), which are the main building blocks of proteins, and sugars (D form), which are the building blocks for carbohydrates and cellulose.

There are 11 enantiomorphic crystallographic point groups and these are listed in the table below:

The active links in this table are simply to remind you of some of the enantiomorphic molecules viewed earlier. If you return to the stereographic diagrams for these point group diagrams, you will see that all of the symmetry related points are of the same handedness, i.e. all the points are shown with open circles only.

Molecules belonging to these groups may exhibit optical activity. The molecule and its enantiomorph rotate the plane of polarisation in opposite senses. (Some molecules belonging to the non-enantiomorphic point groups m, mm2, -4 and -42m may also rotate the plane of polarisation, but this does not give rise to optical activity in the liquid state, owing to the random orientation of the molecules.)

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