An error in ORTEP has been discovered by Dr. Louis Farrugia, the author of Ortep-3 for Windows. The error dates back to the 1976 release of OR TEP-II (ORNL-5138 manual). The result of this error is a reversal of handedness of chiral molecules in ORTEP drawings when BOTH of the following occur:

• All atoms in the atoms list are related by n-fold symmetry with n > 2.

• A 506 instruction (inertial axes coordinate system) is used.

This situation gives a product moment matrix with two equal eigenvalues. When this occurs, the coding error generates a left-handed coordinate system that leads to the incorrect handedness of the ORTEP drawing. Thus, the drawing does not accurately depict the true atomic coordinates input to ORTEP.

We point out that this error is most significant when absolute configuration is being displayed and state again that it only occurs when both conditions listed above are met. The fact that it took 23 years for this error to be discovered suggests the rarity of these conditions in practice.

To extend a famous quote by W. H. Zachariasen - "Don't trust your theoretical models, don't trust your experimental results, [don't trust your computer programs,] and don't take yourself or your work too seriously."

Version 1.0.3 (Jan. 31, 2000) of ORTEP-III corrects the error described above. Check with the authors of software packages that incorporate ORTEP for the status of their programs.

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