The exponential relaxation time constant, T-5, of a nuclear singlet state is influenced by the proximity of neighboring NMR-active nuclei. For methylene groups in particular this dependence is much stronger than the case for other NMR relaxation constants, including the "conventional" relaxation time constant, T-1, of the longitudinal magnetization. This sensitivity provides a new route for determining torsional angles plus other molecular structural details in the isotropic solution phase.