Primary and Secondary Binding Sites for Lanthanide Shift Reagents with Amides. Differential Behavior of cis vs trans Amide Isomers with LSR

Article abstract of DOI:10.1002/mrc.1270140109

Lanthanide induced shifts (LIS) were measured for four dimethylamides, RCON(CH3)2, and four monomethyl amides, RCONHCH3, R=H, CH3, CF3 and CCl3, using Eu(fod)3 in CCl4 and benzene (C6D6) solution.Structural correlations for HCON(CH3)2 and CH3CON(CH3)2 in both solvents yield a preferred binding site for the Eu(fod)3 on one of the lone-pair orbitals of the oxygen atom, with a probable site of secondary importance on the other lone-pair orbital.The cis vs trans isomers of HCONHCH3 and CH3CONHCH3 exhibit remarkably different chemical shift behavior upon addition of Eu(fod)3.