Geometry distorting intramolecular interactions to an alkyne group in 1-(2-aminophenyl)-2-(2-nitrophenyl)ethyne: a joint experimental– theoretical study

Abstract

X-Ray diffraction studies on the title compound show that in the crystalline state the amino and nitro groups lie to the same side of the triple bond and are hydrogen bonded to each other. There is a short contact to each alkyne carbon atom; one from a nitro oxygen atom, which leads to a trans bend in the alkyne, and one from an amino hydrogen atom. The analyses of the ab initio electron densities for this molecule and for its conformer with functional groups lying on opposite sides of the triple bond, using the theory of atoms in molecules, indicate that in both cases there is a bond path and associated (3, –1) critical point between the nitro oxygen atom and the nearer alkyne carbon atom, but not between the amino hydrogen atom and its alkyne carbon neighbour. Plots of the Laplacian for both conformers indicate local concentrations of ‘lone-pair’ density on the nitro oxygen atom, with local depletions in the valence shell charge concentration on the alkyne carbon atom, indicative of a nucleophilelelectrophile type interaction. The geometry of the interaction of the alkyne with the amino hydrogen atom is far from optimal in the trans conformer.