2,6,6-Trimethylcyclohexene-1-carbaldehyde oxime

In the crystal of the title compound C10H17NO, synthesized by the reaction of β-cyclocitral with hydroxylamine hydrochloride, inversion-related molecules are linked by a pair of O—H⋯N hydrogen-bonding interactions between the oxime functionalities, forming R 2 2(6) loops. The molecular conformation is stabilized by intramolecular methyl C—H⋯N interactions. The cyclohexene ring has the typical half-chair conformation.

In the crystal of the title compound C 10 H 17 NO, synthesized by the reaction of -cyclocitral with hydroxylamine hydrochloride, inversion-related molecules are linked by a pair of O-HÁ Á ÁN hydrogen-bonding interactions between the oxime functionalities, forming R 2 2 (6) loops. The molecular conformation is stabilized by intramolecular methyl C-HÁ Á ÁN interactions. The cyclohexene ring has the typical half-chair conformation.
PTM and SJJ thank the DST India (FIST programme) for the use of the diffractometer at the School of Chemistry, Bharathidasan University, Tiruchirappalli, Tamilnadu, India.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ZS2144).

Comment
An oxime is an important functional group in organic chemistry because it is not only used as an efficient protecting group for carbonyls but also may be used for the purification of carbonyl compounds (Donaruma & Heldt, 1960). Moreover oximes are used for the preparation of many compounds such as amines by reduction (Cerny et al., 1969), nitro compounds by oxidation, amides by the Beckmann rearrangement and carbonyl compounds from non carbonyl compounds (Touster, 1953). The title compound C 10 H 17 NO is a key intermediate in the synthesis of aroma compounds such as β-cyclogeranyl nitrile which can be used for the synthesis of the important aroma compound β-damascone (Kutney et al., 1992). Herein, we report the crystal structure of the title compound ( Fig. 1) in which each molecule is connected to an inversion-related molecule through O-H···N hydrogen bonds, (Table 1) forming a cyclic dimer [graph-set R 2 2 (6) (Etter et al., 1990;Bernstein et al., 1995] (Fig. 2). These cyclic DA-AD (Donor Acceptor-Acceptor Donor) interactions involving pairs of O-H···N hydrogen bonds between the oxime functionalities are similar to the O-H···O interactions observed in carboxylic acid dimers. The crystal structure is stabilized by intramolecular methyl C-H···N oxime hydrogen-bonding interactions.

Experimental
To a mixture of 4.6 g (0.065 mol) of hydroxylamine hydrochloride in 50 ml of H 2 O and 10 g (0.065 mol) of β-cyclocitral, a solution of 3.5 g (0.033 mol) of sodium carbonate in 15 ml of H 2 O was added dropwise. The mixture was stirred at room temperature for ten minutes and the solid product which formed was collected and recrystallized from hexane.

Refinement
The H atoms attached to C7 and O1 were located from a difference Fourier map and were refined freely. The remaining H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances in the range 0.93-0.97 Å, and with U iso (H) set at 1.2U eq (C) except for the methyl hydrogen atoms which were refined with U iso (H) set at 1.5U eq (C). Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids drawn at the 50% probability level.  (7) −0.0063 (7) −0.0171 (7)  C10 0.0491 (7) 0.0496 (7) 0.0859 (11) −0.0041 (5) −0.0184 (7) −0.0100 (6) Geometric parameters (Å, °)