Structure, Z′ = 2 Crystal Packing Features of 3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one

3-(2-Chlorobenzylidene)-5-(p-tolyl)furan-2(3H)-one (1), C(18)H(13)ClO(2), crystallizes with Z = 8 and Z′ = 2, and the structure at 100 K has orthorhombic (Pna2(1)) symmetry. Each kind of molecule takes part in π–π stacking interactions to form infinite chains parallel to the c axis. We believe that the existence of two forms can be explained by the probable rotation around a single C–C bond. The quantum chemical modeling reveals that these molecules are almost equivalent energetically, and they can be described as the two most stable conformers (rotamers) with a minor rotational barrier of about 0.67 kcal/mol.