Recognition and use of systematically aberrant phase relationships

Conventional application of direct methods sometimes fails because of systematically aberrant triples. The structure of 8-nitro-l-naphthonitrile, C11H6N2O2, provides an example. Here the procedure of Thiessen & Busing [Acta Cryst. (1974), A30. 814-821] could be used to identify such aberrant triples. The trial structure could then be found straightforwardly. Some situations where aberrant triples may cause trouble are discussed.