The pattern and relative rate of abstraction reactions of tert-butoxyl radicals with fourteen cyclic alkanes and cyclic ethers have been investigated by the aminoxyl radical trapping technique. Oxygen α to C-H strongly enhances abstraction, but β to C-H generally retards abstraction. The rate of abstraction of hydrogens α to oxygen in cyclic ethers was found to decrease with ring size in the order 5 > 7 ≫ 6 > 4. The results are discussed in terms of ring size, abstraction position relative to ethereal oxygen atoms in the ring and aliphatic substitution. Factors such as polarity, torsional strain, hybridisation of the oxygen (whether sp2 or sp 3) and the anomeric effect are considered.