Nuclear Magnetic Resonance Shift Reagents. Quantitative Estimates of Contact Contributions to Lanthanide-Induced Chemical-Shift Changes for exo-Norbornylamine

The possibility of contributions from contact interactions to the predominantly dipolar-induced changes in chemical shifts produced by lanthanide-shift reagents has been widely recognized. Such contributions might be expected to be especially large at the substrate atom directly coordinated to the lanthanide and, in general, be confined with saturated substrates at least to carbons and hydrogens in the immediate vicinity of the coordination site. Nonetheless, there is no firm basis for the prediction of the direction or magnitude of contact contributions to lanthanide-induced shifts on carbon or proton spectra.