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organic compounds
1r,9t,16t-Trioxahexaspiro[2.0.3.0.2.0.3.0.2.0.3.0]heneicosane, C18H24O3, with alternating three- and four-membered rings is mirror-symmetric. Its structure agrees well with that of the parent hydrocarbon. Notable features are the strongly alternating bond angles within the cyclohexane ring and the different bond lengths within the cyclobutane rings.