Phenylhydrazone derivatives of dimedone: hydrogen bonding, spectral (13C and 1H nuclear magnetic resonance) and conformational considerations. Crystal and molecular structures of 5,5-dimethylcyclohexane-1,2,3-trione 2-(4-methylphenylhydrazone)(1) and 5,5-dimethylcyclohexane-1,2,3-trione 2-(4-nitrophenylhydrazone)(2)

Abstract

A series of phenylhydrazone derivatives of 5,5-dimethylcyclohexane-1,3-dione (dimedone) have been prepared. Their i.r. and ¹H n.m.r. spectra are discussed in terms of the extent of intramolecular hydrogen bonding. With o-nitro-group substituents on the aromatic ring, enhanced low-field chemical shifts of the order δ_NHca. 15–16 imply a bifurcated hydrogen bonding environment. Compound (1), C₁₅H₁₈N₂O₃, is monoclinic, space group P2₁/n, Z= 4, cell dimensions a= 14.053(8), b= 5.84(1), c= 16.789(7)Å, β= 98.9(1)°. Compound (2), C₁₄H₁₅N₃O₅, is triclinic, space group P, Z= 2, a= 7.20(1), b= 13.45(1), c= 7.45(1)Å, α= 97.97(5), β= 94.24(5), γ= 98.29(5)°. Both structures were solved by the statistical method and refined using full-matrix least-squares. The numbers of reflections used in the refinement and the final R values are 853, 0.087 and 1 638, 0.078 for (1) and (2) respectively. In (2), the NO₂⋯ HN and CO ⋯ HN separations confirm the o-nitro-involvement in bifurcated intramolecular hydrogen bonding only. In both structures, the cyclohexane ring has an envelope conformation with the C-13 atom 0.68 Å from the plane of the other five.