NMR spin–lattice relaxation time measurements in organochalcogen compounds

¹H and ⁷⁷Se spin-lattice relaxation times have been measured for the series of organochalcogen compounds MeE(CH₂)nEMe (E=S, Se, n=0–3; E = O, n = 1, 2). The methyl and methylene proton T₁ values decreased with increasing mass/size of the chalcogen and with increasing methylene chain length. The values are primarily due to intra- and inter-molecular dipole-dipole relaxation with proton-proton cross-relaxation effects playing a significant role. ⁷⁷Se T₁ values are dominated by spin rotation and chemical shielding anisotropy mechanisms, their relative importance depending on the size of the molecule and temperature of measurement.