Crystal structures of three isomeric forms of hydoxyphenyl-2-oxazoline

The crystal structures of three positionally isomeric compounds, 2-(2-hydroxyphenyl)-2-oxazoline, C9H9NO2, (I), 2-(3-hydroxyphenyl)-2-oxazoline, C9H9NO2, (II), and 2-(4-hydroxyphenyl)-2-oxazoline, C9H9NO2, (III), [alternative names of the title compounds are: 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (II), and 4-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (III)] have been determined. The title compounds were prepared in the course of our research focused at cyclic imino ethers and their utilization in polymer chemistry because hydroxyphenyl-2-oxazolines are known to produce poly(ether-amides) on heating of the monomer. In these compounds, the deviation from coplanarity of oxazoline and benzene rings is dependent on the position of the hydroxyl group at phenyl moiety. The coplanar arrangement in (I) is stabilized by a strong intramolecular O-H...N hydrogen bond. In (II) the hydroxyl group is hydrogen bonded to the ring nitrogen atom on adjacent molecule.Surprisingly, the 2-oxazoline ring of one molecule in asymmetric unit of (II) adopts 3T4 (C2TC3) conformation, while 2-oxazoline ring in the other molecule, as well as that in (I) and (III), is nearly planar, as expected. Tetramers of molecules of (II) are formed and they are bound together via weak C-H...N hydrogen bonds. In (III), strong intermolecular O-H...N hydrogen bonds and weak intramolecular C-H...O hydrogen bonds lead to the formation of an infinite chain of molecules perpendicular to the b direction. The theoretical investigation of H-bonds, based on density functional theory (DFT) employing periodic boundary conditions, has been done using Vienna Ab initio Simulation Package (VASP).