The influence of crown ethers on cation migration processes. Part 7.¹ The 2‐pivaloyl‐1,4‐benzoquinone radical anion

Abstract

The 2-pivaloyl-1,4-benzquinone radical anion has been prepared by alkali metal reduction in tetrahydrofuran in the presence of dibenzo-l&crown-6, 15-crown-5, or 12-crown-4, and its ESR spectrum in each system has been recorded over a range of temperatures. Line-width variation in the ESR spectrum is observed in some systems. This line-width variation has been attributed to cation migration between sites adjacent to the non-equivalent carbonyl groups rather than to restricted rotation of the pivaloyl group. In some systems, however, the rate of migration is too fast and in others too slow, compared with the time-scale of the ESR experiment, for line-width variation to be observed. The influence of each crown ether upon the rate of cation migration has been found to depend upon the size of the crown ether 'cavity' compared with the size of the alkali metal counter-ion.