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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.
Childs et al. (Mon,) studied this question.