Solvent-solute interactions of isomeric phthalaldehydes in aqueous solutions

Combination of electrochemical and spectrophotometric evidence proved that 1,3-benzenedicarboxaldehyde is less than 3% hydrated and 1,4-benzenedicarboxaldehyde is 24% present as geminal diol. Strong hydration indicates a strong resonance interaction between the two CHO groups in para position. Polarographic investigation demonstrated that in aqueous solution the 1,2-benzenedicarboxaldehyde (orthophthalaldehyde) is present in about 10% in unhydrated, about 20% in an acyclic monohydrated and in 70% in a cyclic hemiacetal form. The latter is generally assumed to be the only form present.