Determining an absolute configuration
X-ray crystal structure resolution

Since diffraction intensity is measured, the sign of the phase is unknown: this is Friedel's law. A change in the sign of the phase can be made mathematically by transforming all x y z values into $\overline{x}$$\overline{y}$$\overline{z}$ . It is therefore impossible, when studying a body with an asymmetric carbon, to choose between the two absolute configurations linked to each other by symmetry with respect to a point.

However, Bijvoet found...