Reinvestigation of the structure of 2-hydroxyquinoxaline

Abstract

C₈H₆N₂O, M_r=146.15,orthorhombic, P2₁2₁2₁, a=4.354(1), b=7.348(1), c=21.320(1)Å,V=682.13ų, Z=4, D^x= 1.43,D^m=1.41 Mgm^-3, λ(Cu Kα)=1.5418Å, μ= 7.6mm^-, F(000)= 304 at room temperature, R == 0·041 for 771 observed reflections[1>3σ(I)].A reinvestigation of (he structure of 2·hydroxyqumoxaline based on diffrac­tioncmctcr data has yielded more precise structural parameters (bond-length and angle e.S.d.'s of 0·004 Å, 0·2°) than the photographic results of Stepien, Grabowski, Cygler & wajsman [(1976).Acta Cryst. B32, 2048-2050] (R = 0·110, bond-length and angle e.s.d.ts 0·01 Å. O· 7⁰). The compound exists in the keto form in the crystal with C=O = 1·239 (3)Å . The quinoxaline rings arc essentially planar (inter-ring dihedral angle,1·6°) including the exccyclic atoms. The large deviation of H(5) from the ring plane (0·59 Å ) reported earlier is not observed here. The crystal structure is stabilized by strong intermolecular hydrogen bonds: N .. ·O = 2·782 (6) Å , N-H .. ·O = 162°.