Crystal structure and conformational analysis of 2-hydroxy-3-(2-methylprop-1-en-1-yl)naphthalene-1,4-dione

In the structure of the naphthoquinone derivative 2-hydroxy-3-(2-methylprop-1-en-1-yl)naphthalene-1,4-dione, the molecules form a centrosymmetric cyclic dimer through intermolecular O—H⋯O hydrogen bonds which, together with intermolecular C—H⋯O hydrogen bonds and weak π–π ring interactions, give rise to an overall two-dimensional structure.

In the structure of the title compound, C 14 H 12 O 3 , the substituent side chain, in which the H atoms of both methyl groups are disordered over six equivalent sites, lies outside of the plane of the naphthalenedione ring. The ring-to-chain C-C-C-C torsion angles are 50.7 (3), À176.6 (2) and 4.9 (4) . An intramolecular methyl-hydroxy C-HÁ Á ÁO hydrogen bond is present. In the crystal, molecules are primarily connected by intermolecular O-HÁ Á ÁO hydrogen bonds, forming a centrosymmetric cyclic dimer motif [graph set R 2 2 (10)]. Also present is a weak intermolecular C-HÁ Á ÁO hydrogen bond linking the dimers and a weakring interaction [ring centroid separation = 3.7862 (13) Å ], giving layers parallel to (103).

Figure 2
The centrosymmetric dimers formed from the O3-HÁ Á ÁO1 i hydrogen bonds, viewed (a) along a and (b) along b. For symmetry code (i), see Table 1.

Figure 3
The crystal packing in the unit cell, showing intra-and intermolecular interactions as dashed lines.

Figure 1
Molecular conformation and atom-numbering scheme, with non-H atoms drawn at the 50% probability level. The H atoms of the rotationally disordered methyl groups are shown as six equivalent half-occupancy sites.
moiety. There are structures similar to the title compound, whichvary depending on the oxidant used in the synthesis.

Synthesis and crystallization
The compound was obtained through to the lapachol oxidation product as can be seen in the scheme below (Hooker, 1936). The sample was subjected to an ethyl acetate solution at 301 K for crystallization.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The O3-bound H atom was located in a difference Fourier map and was freely refined. The remaining H atoms were positioned geometrically with aromatic C-H = 0.93 Å and U iso (H) = 1.2U eq (C). Rotational disorder was identified in the hydrogen atoms of the methyl carbon atoms C12 and C22 and these were included in the refinement over six equivalent 60 sites with 50% occupation, with C-H = 0.96 Å and U iso (H) = 1.5U eq (C).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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 Occ. (