Novel Synthesis and Crystal Structures of Two α, α′-bis-Substituted Benzylidene Cyclohexanones: 2,6-Bis-2-nitro(benzylidene)cyclohexanone and 2,6-Bis-4-methyl(benzylidene)cyclohexanone

Abstract

Two α,α′-bis-substituted benzylidene cycloalkanones have been synthesized in presence of SnCl4 and their crystal structures have been determined by means of X-ray diffraction. The bis(para-methyl) derivative, 2,6-bis-4-methyl(benzylidene)cyclohexanone 1 crystallizes in the orthorhombic space group Pbca with a = 9.413(2) A, b = 10.787(2) A, and c = 33.702(5) A, while bis(ortho-nitro) derivative, 2,6-bis-2-nitro(benzylidene)cyclohexanone in monoclinic P21/n space group with a = 8.482(2) A, b = 13.435(2) A, c = 15.377(3) A, and β = 92.96(2)°. In both compounds the olefinic bonds are in E-configuration, and the cyclohexyl rings adopt a sofa conformation. The phenyl rings are not coplanar with the planes of C=C–C(=O)–C=C fragments; the dihedral angles between these planes are 14.25(11) and 19.37(11)° in 1 and 60.50(6) and 63.26(6)° in 2. This twist might be regarded as the effect of the repulsive interactions between the hydrogen atoms from phenyl and cyclohexyl rings, and much larger values in 2 are certainly connected with the presence of nitro group in ortho-positions of the phenyl ring. It seems that, because of the lack of specific interactions the close packing requirements and the van der Waals forces are main factors determining the crystal packing. The phenyl rings are not coplanar with the planes of C=C–C(=O)–C=C fragments as the effect of the repulsive interactions between the hydrogen atoms from phenyl and cyclohexyl rings .