The Lewis acid complexes of ,-unsaturated carbonyl and nitrile compounds. A nuclear magnetic resonance study

1:1 Complexes of a range of Lewis acids with crotonaldehyde (1) have been systematically investigated by 1 H and 13 C nmr spectroscopy. Lewis acids employed were: BF 3 , BCl 3 , BBr 3 , SnCl 4 , TiCl 4 , SbCl 5 , AlCl 3 , EtAlCl 2 , Et 2 AlCl, Et 3 Al 2 Cl 3 , and Et 3 Al. Chemical shift changes in 1 H nuclei remote from the Lewis acid group were found to be remarkably regular and consistent. The study has been extended to tiglaldehyde (2), pent-3-en-2-one (3), cyclohexenone (4), methyl crotonate (5), and crotonitrile (6) and the relationships between the chemical shift differences associated with complexation of these have been explored.