Facile synthesis, spectroscopic characterization and X-ray analysis of 4-alkoxylated 2-hydroxybenzophenones

Two 2-hydroxy-4-alkoxy-3′-nitrobenzophenones were synthesized in a facile way. Their structures were characterized with the aid of mass spectra and 1H NMR spectra analysis, as well as X-ray diffraction analysis. The 1H NMR spectra showed an intramolecular hydrogen bond formation in their structures. Compound 1 crystallizes in the monoclinic P2 (1) space group with the crystal cell parameters a = 3.9318(4) Å, b = 7.1042(9) Å, c = 22.0400(19) Å, α = 90.00°, β = 92.3140(10)°, γ = 90.00°, V = 615.13(11) Å3 and Z = 2. Compound 2 crystallizes in the monoclinic space group P2 (1)/n with the crystal cell parameters a = 3.9765(5) Å, b = 11.8286(15) Å, c = 28.867(3) Å, α = 90.00°, β = 92.8710(10)°, γ = 90.00°, V = 1356.1(3) Å3 and Z = 4. Results showed that the benzophenone skeletons are non-planar, with a large torsion to minimize their repulsive force. The substituted nitro or alkoxy groups are essentially coplanar with respect to the benzene rings to which it connected, whereas the carbonyl group in benzophenone skeleton is coplanar with the benzene ring which is substituted by alkoxy group. Classic and non-classic intra- and intermolecular hydrogen bonds, together with the π–π stacking interactions stabilize their molecular conformations. The minor variations in the alkoxy group substituent cause great difference in their intermolecular hydrogen bond formation and stacking mode.