The inversion operation occurs through a single point called the inversion center, i, located at the center of the molecule. (Note that the inversion center may or may not coincide with an atom in the molecule.) Each atom in the molecule is moved along a straight line through the inversion center to a point an equal distance from the inversion center. If the resulting configuation is indistinguishable from the original, we say there exists an inversion center in the molecule.
Each of the following molecules contains an inversion center: