Crystal structure of 2,2-dichloro-1-(piperidin-1-yl)ethanone

In the title compound, C7H11Cl2NO, the piperidine ring shows a chair conformation and the bond-angle sum at the N atom is 359.9°. The H atom of the dichloromethyl group is in an eclipsed conformation with respect to the carbonyl group (H—C—C=O = −5°). In the crystal, inversion dimers are linked by pairs of C—H⋯O hydrogen bonds between the dichloromethyl group and the carbonyl O atom, which generate R 2 2(8) loops. The dimers are linked into a ladder-like structure propagating in the [100] direction by short O⋯Cl [3.1084 (9) Å] contacts.


S1. Comment
The title compound is an intermediate in the synthesis of 2,2-dimethoxy-1-(pyridin-2-yl)ethanone and has been synthesized from 2,2-dichloro-1-(piperidin-1-yl)butane-1,3-dione (Schwierz et al., 2015) following a modified procedure (Schank, 1967). As it is expected the piperidine ring shows a chair conformation and the amide substructure is planar. The hydrogen atom of the dichloromethyl group is in an eclipsed conformation with respect to the carbonyl group. In the crystal structure, dimeric aggregates are formed by hydrogen bonds of the C-H···O type between the dichloromethyl group and the carbonyl oxygen atom. In addition, these dimers are linked into a ladder-like structure parallel to the ac plane by oxygen chlorine contacts.

S2. Experimental
22 ml methanol was cooled down to -6°C and then 1.93 g (84 mmol) sodium was slowly added in a way that the temperature is maintained. Afterwards 20.0 g (84 mmol) 2,2-dichloro-1-(piperidin-1-yl)butane-1,3-dione in 10 ml methanol was dropwise added to the solution of NaOMe. The resulting solution was stirred for 30 minutes and then neutralized with aqueous HCl at -10°C. After evaporating the mixture to dryness the amorphous material was collected on filter paper in a Büchner funnel and washed with water (yield: 13.6 g, 83%). The product has to be destilled in vacuo (0.2 mbar) and condensed into a Schlenk tube cooled by liquid nitrogen to obtain colourless prisms for X-ray diffraction.

S3. Refinement
The positions of all hydrogen atoms have been determined from a Fourier map and all hydrogen atoms were refined without any constraints.

Figure 1
Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Crystal structure of the title compound showing ladder-like arrangement parallel to the ac plane. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.36 e Å −3 Δρ min = −0.18 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.