EFFECTS OF SOLVENT AND TEMPERATURE ON MAGNETICALLY NONEQUIVALENT METHYLENE PROTONS IN ASYMMETRIC PHOSPHORUS COMPOUNDS

The high-resolution nmr spectra of compounds of type p-NO2C6H4O)P(O)(CH3)(OCH 2COC6H4-p-Y where Y is H Cl, CH3, NO2, and OCH3 have been studied as a function of solvent and temperature. Solvents with high dielectric constants (DMSO-d6) give equivalent methylene protons while solvents of low dielectric constants (CDCl3) give magnetically nonequivalent methylene protons. When magnetic nonequivalence is observed, the methylene protons form the AB part of an ABX spin system where X is the phosphorus nucleus. A two-conformer model is used to fit the observed temperature dependence. The activation energy obtained is comparable to the temperature dependence of the dielectric constant of the medium.