The ground state 1 A of N-methylene-N-oxide-methanamine or N-methylnitrone has C s symmetry; the three-fold methyl rotor has a barrier of 6.9 kJ mol -1 . Lukomska et al. discuss the nature of the bonding in this compound and show that the N -O bond in this acyclic N-oxide should be considered as a single dative bond N ⊕ →O with only a negligible contribution from a double bond. Furthermore they show that although primarily a single bond the NO bond is significantly shorter at 1.266 Å (here 1.262 Å) and stronger at 556 kJ mol -1 than other cyclic N-oxides. Komaroni et al. argue that the electronic structures of the nitrones cannot be represented by one well-defined Lewis-type structure but instead are a mixture of the zwitterionic and the hypervalent. Other nitrones are possible, for example a C-methyl nitrone rather than an N-methyl, Fig. , with E and Z conformers. The order of stability is