Abstract
Factors affecting the spin-lattice relaxation times T 1 of 13C resonances at 62.9 MHz were investigated for simple mixtures of tetralin, ethylbenzene, pentane and phenol and the prominent resonances of an anthracene oil and a coal-derived hydrogenation oil. Parameters varied were solvent temperature and nature—Cr(acac) 3, Cr(dpm) 3, Cr(hfac) 3, Fe(acac) 3, Fe(dpm) 3—and concentration of a paramagnetic relaxation agent (PARR). Effects of PARRs on relaxation rates are strongly dependent on neighbouring acidic or basic centres, but are much more uniform for Cr(hfac) 3 than for Cr(acac) 3. The presence of basic or acidic compounds does not significantly affect the relaxation of 13C of the neutral components. Optimum experimental conditions are characterized by nearly uniform T 1 values of all resonances to be detected. While 2D spectra allow disentanglement of overlapping lines, choosing optimum conditions for the neutral constituents may lead to a loss of signals from the acidic or basic compounds.
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