A number of ketyls and semidiones containing13C have been examined by ESR spectroscopy. Grossly different values ofaCOCin the ketyls (sim;thinsp;50 G) and the semidiones (sim;thinsp;1 G) allow for an easy differentiation of the two species. This is important because strained ring ketyls can undergo a decomposition reaction leading to the semidione with one additional carbonyl group added to the ketyl. Values ofaCOC, aagr;C,andabgr;Cfor keyls and semidiones are reporduced by the Karplusndash;Fraenkel equation if the termQCCprime;Cis allowed to increase by 15percnt; when Cprime; is altered from methyl tothyphen;butyl. No evidence for the nonplanarity of dihyphen;thyphen;butyl ketyl could be deduced. Some unusual longhyphen;range13C hfsclpar;aggr;Crpar;have been detected in certain bicyclic semidiones possessing a nearly coplanar, zigzag arrangement of three carbonndash;carbon bonds with apzorbital.
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