We next investigated Tm across a range of temperatures. A plot of Tm as a function of temperature (Figure ) clearly shows how methyl rotation significantly increases relaxation in tetramethyl nitroxide 12 (from 80 K) and tetraethyl nitroxide 13 (from 60 K). The earlier onset of methyl rotation in tetraethyl nitroxides is explained by a lower energy barrier of methyl rotation in these systems. It is not clear, however, why the Tm apparently increases again, and becomes longer than the tetramethyl nitroxide 12 as the temperature rises above ca. 120 K. This unexpected behaviour is in line with observations in our previous work, and suggests further complications connected with the use of tetraethyl nitroxides. The origins of this effect will be further investigated in the future.