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The spin-spin coupling constants 3JC,H between the hydrogen atom of the aldonitrone group and the carbon atom bound to the nitrogen atom of the N-oxide fragment were determined for a wide range of cyclic and acyclic aldonitrones. Based on comparison of these constants (trans-3JC,H (E isomer) > cis-3JC,H (Z isomer)), the Z configuration was assigned to acyclic nitrones. Coordination of organolithium compounds to the oxygen atom of the N→O group was revealed by 13C NMR spectroscopy. This coordination is the necessary condition for the metallation of aldonitrones. The configuration of the nitrone group is responsible for the ability of the E form of acyclic aldonitrones to undergo CD3ONa-catalyzed isotope exchange of the methine proton in CD3OD and metallation with BusLi.