Applications of lanthanide induced shift NMR experiments to the structure determination of organic molecules

The problem of using lanthanide induced shift (LIS) data to determine the structure of organic molecules is attacked by considering the following topics. I. How can LIS indices best be determined? II. Should the observed shifts be factored into contact and pseudocontact contributions? III. Is the use of the McConnell-Robertson relationship for axially symmetric ions appropriate? IV. What orientation of the principal magnetic axis should be used for the computer simulation of the experiment? V. What is the optimum method for matching experimental and calculated LIS values? The results of five methods of determining LIS indices for pyridine and THF are compared. Although the absolute magnitudes of the LIS indices vary from method to method, the set of internally scaled LIS indices are virtually identical. A computational method is developed which is based on the McConnell-Robertson pseudocontact relationship for axially symmetrical ions. An assessment of how well a set of experimental LIS indices fits a given substrate topology is furnished by the agreement factor, R...