(13)C NMR and X-ray Structure Determination of 1-(Arylazo)-2-naphthols. Intramolecular Proton Transfer between Nitrogen and Oxygen Atoms in the Solid State

Article abstract of DOI:10.1021/ja00197a003

The tautomeric reaction involving a single proton transfer in 1-(phenylazo)-2-naphthol and its 4'-methoxy, ethoxy, and N,N-dimethylamino derivatives has been investigated with variable-temperature solution and high-resolution solid-state (13)C NMR spectroscopy.Crystal structures of the parent unsubstituted compound and the 4'-N,N-dimethylamino derivative have been determined.All of these compounds undergo a fast proton exchange on the NMR time scale between the tautomeric azo and hydrazone forms in both solution and the crystalline phase.Equilibrium compositions inthe solid materials are similar to those measured in solution.Crystals of 1-(phenylazo)-2-naphthol are monoclinic, a = 27.875 (7), b = 6.028 (2), c = 14.928 (5) Angstroem, β = 103.57 (2)⁰, the space group is C2/c with Z = 8, and the structure at 213 K was refined to an R factor of 0.0414 on 1082 observed reflections.Crystals of 1-(<4'-(dimethylamino)phenyl>azo)-2-naphthol are monoclinic, a = 7.604 (1), b = 7.970 (3), c = 24.381 (7) Angstroem, β = 99.33 (2)⁰, the space group is P2₁/c with Z = 4, and the structure at 193 K was refined to an R factor of 0.0405 on 1522 observed reflections.