Steric Influences on Spin-Lattice Relaxation Rates of Methyl Protons in Substituted Aromatic Molecules

Article abstract of DOI:10.1002/mrc.1260230803

Proton spin-lattice relaxation rates (R₁ values) have been measured at 400 MHz for a series of substituted aromatic compounds to determine the steric effects of ortho substituents on the R₁ values of the methyl groups.These values have been interpreted on the basis of differences in the barriers to methyl group rotation caused by the substituent, resulting in changes in the contributions from the dipolar and the spin-rotation relaxation mechanisms.A significant dynamic range of methyl R₁ values has been observed, showing that these measurements are sensitive to the steric environment.