On the magnetic non-equivalence of methylene protons in some propane derivatives, and its variation with solvent and temperature

The magnetic non-equivalence, δ ab, of methylene protons in 1,2-disubstituted and 1,2,3-trisubstituted propanes (same substituent) shows a marked dependence on solvent and temperature that allows a correlation with conformational equilibrium. Results indicate that symmetry is a necessary, but not a sufficient, condition for observation of δ ab. Factors that affect rotamer population such as medium, temperature, and nature of substituents, contribute substantially to the magnitude of δ ab.