organic compounds
The racemic title compound, C17H23N3O3, isolated from the reaction of L-(-)-tyrosine hydrazide with triethyl orthopropionate in the presence of a catalytic quantity of p-toluenesulfonic acid (p-TsOH), crystallizes with Z' = 1 in a centrosymmetric monoclinic unit cell. The molecule contains two planar fragments, viz. the benzene and imidazole rings, linked by two C-C single bonds. The dihedral angle between the two planes is 59.54 (5)° and the molecule adopts a synclinal conformation. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates no substantial interaction between the two -electron delocalization regions in the molecule. In the crystal structure, there is an O-HN hydrogen bond that links the molecules along the c axis.
organic compounds
The title compound, C15H11N3O, (I), was obtained by the air oxidation of 3,5-diphenyl-4,5-dihydro-1,2,4-triazin-6(1H)-one. In the crystal structure, (I) forms centrosymmetric hydrogen-bonded dimers through pairs of N—HN hydrogen bonds. The molecular structure of (I) deviates somewhat from planarity in the crystalline state, whereas a density functional theory (DFT) study predicts a completely planar conformation (Cs point-group symmetry) for the isolated molecule. The solid-state conformation of (I) is stabilized by intramolecular hydrogen bonds, viz. one C—HO interaction, which forms a six-membered ring, and three C—HN interactions that each form five-membered rings. To estimate the influence of the intramolecular hydrogen-bonded rings on the aromaticity of the phenyl rings, the HOMA (harmonic oscillator model of aromaticity) descriptor of π-electron delocalization has been calculated for conformations of (I) with and without intramolecular hydrogen bonds. In the planar conformation of (I), the HOMA values for both benzene rings are lower than in hypothetical conformations without intramolecular hydrogen bonds.