1,1,1-Trichloro-2,2-bis(4-ethoxyphenyl)ethane

In the title compound, C18H19Cl3O2, which is the 4-ethoxyphenyl analogue of the insecticidally active 4-methoxyphenyl compound methoxychlor, the dihedral angle between the two benzene rings is 60.38 (13)°. An intramolecular aromatic C—H⋯Cl interaction is present.

In the title compound, C 18 H 19 Cl 3 O 2 , which is the 4-ethoxyphenyl analogue of the insecticidally active 4-methoxyphenyl compound methoxychlor, the dihedral angle between the two benzene rings is 60.38 (13) . An intramolecular aromatic C-HÁ Á ÁCl interaction is present.

Comment
The title compound, C 18 H 19 Cl 3 0 2 is the 4-ethoxyphenyl analogue of the insecticides DDT [1,1,1-trichloro-2,2-bis(4chlorophenyl)ethane] and methoxychlor (the 4-methoxyphenyl analogue), and has similar insecticidal activity (Läuger et al., 1944), but was not used as a commercial product. The crystal structures of methoxychlor (Smith et al., 1976) and the p-butoxy analogue (Smith, 2012) are known and the unit cell data for the title compound has been reported (Schneider & Fankuchen, 1946). The structure of the title compound is reported herein.
The molecular structure of the title compound is shown in Fig. 1. The unit cell and space group are consistent with those previously reported. The dihedral angle between the two benzene ring mean planes is 60.38 (13)°. The value of this angle is 77.7° (no s.u. available) in the structure of methoxychlor (Smith et al., 1976). The conformations of the two ethoxy side chains relative to their benzene rings (A and B) are similar [comparative torsion angles C3-C4-O4-C11, -173.3 (3) and 162.2 (2), respectively]. The B ring conformation is stabilized by an intramolecular aromatic C2B-H···Cl2 interaction (Table 1). No significant intermolecular interactions are present (Fig. 2).

Experimental
The title compound was obtained as an analytical reference standard from the US Public Health Service. Colourless crystal prisms suitable for X-ray analysis were obtained by room temperature evaporation of a solution of the title compound in ethanol.

Refinement
Hydrogen atoms were included in the refinement at calculated positions [C-H = 0.93-0.98 Å, with U iso (H) = 1.2U eq (C) (aromatic, methylene and methine) or 1.5U eq (C)(methyl), using a riding-model approximation.  The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.

Figure 2
A perspective view of the crystal packing in the unit cell viewed approximately along the b axis. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.25 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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