Affordable Access

Publisher Website

Azo—hydrazone tautomerism in azo dyes. III. The tautomeric structure of 1-(4′-nitrophenylazo)-2-naphthylamine from crystal structure determination

Dyes and Pigments
Publication Date
DOI: 10.1016/0143-7208(82)80001-6
  • Chemistry
  • Mathematics
  • Physics


Abstract The structure of 1(NO 2 )—dioxane 2:1 solvate single crystal has been determined by direct methods and refined by analysis of the three-dimensional Mo Kα intensity data. The unit cell is monoclinic, space group P2 1 /c with a = 8·960(3), b = 6·386(2), c = 30·141(11) Å, β = 108·56(2)°. Least-squares refinement of all positional and thermal parameters (hydrogen atoms isotropic) with 1458 independent reflections out of 2817 gave a final R-index of 0·069. The dye molecule is almost planar and of trans configuration. The nitro group, however, is significantly twisted out of the molecular best plane. Six-membered chelate ring structures are formed by intramolecular NH···N bonds while intermolecular NH···O interactions give rise to complex formation involving two dye and one dioxane molecules in a centrosymmetrical arrangement. Two such complexes are accommodated in the unit cell. Based on the observed molecular geometry and quantum chemical (SCF—MO) calculation of bond dimensions a strong predominance of the azo tautomer was concluded for 1(NO 2 ). This assignment is further supported by empirical correlations, using CN and NN bond distances from a great variety of reported azo and hydrazone structures which are compiled here for the first time. The mobile hydrogen is attached to the amine nitrogen [R(NH) = 1·04(5) Å ] thereby excluding a major participation of the hydrazone form. These findings compare well with those for solutions and are in accordance with previous quantum chemical predictions.

There are no comments yet on this publication. Be the first to share your thoughts.