5,6,7,8-Tetrahydroquinoline 1-oxide hemihydrate

In the title compound, C9H11NO·0.5H2O, the asymmetric unit contains two similar molecules of 5,6,7,8-tetrahydroquinoline 1-oxide and one water molecule. The water molecule links the two O atoms of both independent N-oxides into dimers via O—H⋯O hydrogen bonds, forming a three-dimensional network along [101], which is additionally stabilized by weak C—H⋯O intermolecular interactions. In each molecule, the saturated six-membered rings exist in a conformation intermediate between a half-chair and sofa.

The asymmetric unit contains two similar molecules of 5,6,7,8-tetrahydroquinoline 1-oxide and one water molecule (Fig.   1). The water molecule links the two O atoms of both independent N-oxides by O-H···O hydrogen bonds into dimmers, which form a three-dimensional network along the [101] (Fig. 2). Additional weak C-H···O intermolecular interactions help stabilize the crystal packing (Table 1). The water molecule is observed in the 1 H NMR spectrum as a broad signal at 2.4 ppm and in the IR spectrum as two absorption maxima for two different O-H bonds at 3368 and 3312 cm -1 , respectively.
After purification on column chromatography with silica gel and using ethyl acetate, the trace of the substrate was first supplementary materials sup-2 removed. The product was eluted with a mixture of ethyl acetate/methanol (50:1) and colourless crystals were obtained. Yield: 310 mg (83%) and m.p. 344 K. Crystals suitable for X-ray diffraction analysis were grown by slow evaporation of a dichloromethane/hexane (1:10) solution.

Refinement
The H atoms of the water molecule involved in the intramolecular hydrogen bonds were located by difference Fourier

Special details
Experimental .  Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.