Abstract
The results of studies on the structures of equimolar complexes of acyl halides with Lewis acids in the solid state and in solutions are surveyed. The methods for the identification of acylium salts and donor–acceptor complexes as well as the factors influencing the equilibrium between them are examined. Communications reporting the formation of complexes of other types in acyl halide–Lewis acid systems are reported and are discussed critically. The bibliography includes 102 references.