(Z)-6-{[1,3-Dihydroxy-2-(hydroxymethyl)propan-2-yliminio]methyl}-2-ethoxyphenolate, (Z)-6-{[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yliminio]methyl}-4-nitratocyclohexa-2,4-dienone monohydrate and (R,E)-2-[(1-hydroxybutan-2-ylimino)methyl]phenol.

The title compounds C(13)H(19)NO(5), C(11)H(14)N(2)O(6)xH(2)O and C(11)H(15)NO(2), respectively, have been derived from 3-ethoxysalicylaldehyde, 5-nitrosalicylaldehyde and salicylaldehyde, respectively. The C-O and N-C bond distances, and three hydrogen bonds formed by the phenolate O atom, show that the zwitterionic form exists in the first compound. The second compound is transformed to the quinoid form as a result of resonance between the zwitterionic form and the nitro group. The third compound exists in the phenol-imine form, with appropriate C-N and C-O bond distances.