Abstract Boron trihalides are used widely in chemistry as typical Lewis acids. It is well known that the acid strength of boron trihalides increases in the order BF3 3 3. This ordering, however, is contrary to that expected from electronegativity differences and steric effects arguments, which suggest that boron trifluoride should be the strongest Lewis acid in the series. Much effort, particularly from the theoretical side, was devoted to shed light on this apparent controversy. In the present contribution the different theoretical studies have been compared.
