3-[(E)-2-(2-Methoxyphenyl)vinyl]-5,5-dimethylcyclohex-2-enone

The title compound, C17H20O2, has an E conformation about the bridging C=C bond. The cyclohexene ring adopts an envelope conformation with the dimethyl-substituted C atom as the flap. Its mean plane makes a dihedral angle of 7.20 (12)° with the benzene ring. In the crystal, neighbouring molecules are connected via C—H⋯O hydrogen bonds, forming chains running along the a-axis direction.

The title compound, C 17 H 20 O 2 , has an E conformation about the bridging C C bond. The cyclohexene ring adopts an envelope conformation with the dimethyl-substituted C atom as the flap. Its mean plane makes a dihedral angle of 7.20 (12) with the benzene ring. In the crystal, neighbouring molecules are connected via C-HÁ Á ÁO hydrogen bonds, forming chains running along the a-axis direction.
In the crystal, hydrogen bonded chains running along the a-axis direction are generated by connecting neighbouring molecules via C-H···O hydrogen bonds (Table 1 and Fig. 2).

Experimental
A mixture of isophorone (0.01 mol), 2-methoxybezaldehyde (0.01 mol) and sodium hydroxide solution (10 ml, 10%) in ethanol (25 ml) was stirred at room temperature until the starting material disappeared. The resulting mixture was poured into crushed ice and the precipitate was filtered off, dried and recrystallized from ethanol giving p. colourless block-like crystals [Yield = 93%; M.p. = 373-375 K].

Refinement
The H atoms were placed in calculated positions and refined as riding atoms: C-H = 0.93 -0.97 Å with U iso (H) = 1.5U eq (C-methyl ) and = 1.2U eq (C) for other H atoms.  The molecular structure of the title molecule, with atom labelling. The displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the title compound viewed along the b axis. The hydrogen bonds are shown as dashed lines (see Table 1 for details; H-atoms not involved in hydrogen bonding have been excluded for clarity).  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.65 e Å −3 Δρ min = −0.27 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1