Molecular Motion in Liquids: The Partially Rigid Molecule 1,2,3,4-Tetrahydro-5,6-Dimethyl-1,4-Methanonaphthalene. Temperature Dependence of 13C Magnetic Relaxation and Correlation Times

Abstract

For the hydrocarbon 1,2,3,4-tetrahydro-5,6-dimethyl-1,4-methanonaphthalene (5,6-Me2-THMN) 13C longitudinal relaxation times and NOE factors were measured over a wide temperature range at frequencies of 22.63 and 100.62 MHz. Additionally, 13C transversal relaxation times were measured at 100.62 MHz. The relaxation data show that the dispersion region is already reached at moderate temperatures. The experimental data were modeled by the combination of the Vogel- Fulcher-Tammann ansatz and a scaling of the dipolar coupling constant with a factor of 0.70. From the fit of the data also activation parameters of the rotational motion of the molecules were obtained. Although the molecules of 5,6-Me2-THMN have a rigid structure (except the two internally rotating methyl groups), the model of the rotational diffusion of rigid bodies does not satisfactorily describe the relaxation data.