Structure elucidation with lanthanide induced shifts. 7—development of a reliable method for structure evaluation and the application to organic nitriles

A useful and reliable procedure has been developed for the evaluation of the structures of organic nitriles using lanthanide shift reagents. The procedure is based on a statistical comparison of the experimental lanthanide induced shifts (LIS) with values which are predicted with the pseudocontact equation for a proposed structure. The experimental LIS are obtained by nonlinear regression analysis of the chemical shifts observed in the presence of varying amounts of the shift reagent, Eu(fod) 3 . The precise geometry for a proposed structure is obtained from molecular mechanics calculations. The LIS are then predicted with the pseudocontact equation using k =976.6 and a europium‐nitrogen bond length of 2.50 Å. (Detailed arguments are presented in support of these values.) The carbon‐nitrogen‐europium array is approximately linear, although small distortions from linearity are both expected and observed.