How Do Spin-Orbit-Induced Heavy-Atom Effects on NMR Chemical Shifts Function? Validation of a Simple Analogy to Spin-Spin Coupling by Density Functional Theory (DFT) Calculations on Some Iodo Compounds

Spin–orbit coupling is responsible for many heavy-atom effects on NMR chemical shifts, for example, normal halogen dependence. A simple but general model for spin–orbit-induced substituent effects has now been developed by analogy to the Fermi contact spin–spin coupling mechanism (see below). DFT calculations on some simple iodo compounds illustrate the scope and validity of the model.