Crystal and molecular structure of 10,10-dimethyl-3,4-dioxatricyclo-[5.2.1.0]decane-2-spiro-2′-adamantane and a comparison of C–O and O–O bond lengths in small rings as a function of ring size

The crystal structure of the title compound (IV) formed by reaction of singlet oxygen with camphenylideneadamantane (I) shows it to be a 1,2-dioxolan in which the camphane framework has rearranged to norbornane. Crystals are orthorhombic, space group P212121, with a= 23.17(2), b= 9.76(1), c= 6.74(1)A, Z= 4; the structure was refined to R 0.062 based on 783 counter reflections. From comparisons with other structures it is shown that in small-ring cyclic peroxides and related molecules the C–O and O–O follow the trend of C–C bonds in being longer in four- than in either three- or five-membered rings. However the differences in bond length with ring size appear to be larger for C–O and smaller for O–O bonds by comparison with C–C bonds.