Carbon‐13 NMR. The analysis of the relaxation times T1 of benzofuran and of a series of its methyl derivatives. Correlations between molecular motions and structural properties

Carbon‐13 relaxation times (T1) and nuclear Overhauser enhancements (η) have been measured for benzofuran and a series of its methyl derivatives. The contributions of dipolar (T1 DD) and spin rotation (T1SR) mechanisms have both been determined. The temperature dependence of T1 has been studied. The relationships between molecular motions and structural properties have been emphasized. The overall motional anisotropy of the benzofuran molecule is increased by substitution in positions 2 and 5. The internal rotation of a methyl group may change depending on its position in the molecule and on the influence of other methyl groups in its close neighbourhood.