Crystal structure of (E)-2-[(2S,5R)-2-isopropyl-5-methylcyclohexylidene]hydrazine-1-carbothioamide

The title compound, C11H21N3S, consists of a menthone moiety attached to an extended thiosemicarbazone group with the N—N—C—N torsion angle being 11.92 (16)°. The cyclohexane ring has a chair conformation and the conformation about the C=N bond is E. In the crystal, molecules are linked via pairs of N—H⋯S hydrogen bonds, forming chains along the a axis. The absolute structure could be assigned with reference to the starting material, i.e. enantiopure (−)-menthone [Flack parameter = 0.05 (5)].

In the molecular structure of the title compound, Fig, 1, the thiosemicarbazone unit is not completely planar, but shows a torsion angle N1-N2-C11-N3 of 11.92 (16)°. The cyclohexane ring of the menthone unit is in the chair conformation.
The molecule, shows also a trans conformation about the N1-N2 bond.
For the synthesis, enantiopure (-)-menthone was used. No change in chirality occurred in the course of the reaction with thiosemicarbazide and the obtained product emerged as chiral crystals in the non-centrosymmetric space group P2 1 2 1 2 1 .
In the crystal, molecules are connected by a pair of N-H···S hydrogen bonds, with bridging sulfur atoms, into a onedimensional chain along the a-axis ( Fig. 2 and Table 1).

S2. Synthesis and crystallization
The synthesis of the title compound was adapted from a previously reported procedure (Freund & Schander, 1902). In a hydrochloric acid catalyzed reaction, a mixture of (-)-menthone (10 mmol) and thiosemicarbazide (10 mmol) in ethanol (80 ml) was refluxed for 5 h. After cooling and filtering, the title compound was obtained. Colourless needles were obtained by slow evaporation of a solution in the solvent DMSO.

S3. Refinement
All the H atoms were located in a difference Fourier map and freely refined. The assignment of the correct absolute configuration was assured by the Flack parameter of 0.05 (5).

Figure 1
The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 40% probability level.

Figure 2
A partial view along the c-axis of the crystal structure of the title compound, showing the hydrogen bonded chains (hydrogen bonds are shown as dashed lines; see Table 1 for details). KappaCCD Graphite monochromator Detector resolution: 9 pixels mm -1 CCD rotation images, thick slices scans Absorption correction: analytical (Alcock, 1970) T 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 −0.08952 (