On the molecular structure of (E)-3-(9H-fluoren-2-yl)-1-(pyridin-2-yl) prop-2-en-1-one, theoretical calculations and SXRD studies

The azachalcone, (E)-3-(9H-fluoren-2-yl)-1-(pyridin-2-yl)prop-2-en-1-one (C21H15NO) (3) was synthesized by classical Claisen-Schmidt condensation reaction. An E-configuration was confirmed through single-crystal X-Ray diffraction studies; crystallizing in monoclinic space group P 2(1)/c, with unit cell parameters a = 16.115 angstrom (3), b = 12.277 angstrom (3), c = 7.6884 angstrom (15) and Z = 4. Our approach to correlate the experimental molecular structure with the NMR assignment of this azachalcone comprised DFT computations of magnetic shielding, coupled with 2D-NMR spectroscopy. With a correlation of R-2 = 0.9965 between experimental and computed C-13-NMR chemical shifts, this strategy allowed the full C-13 assignment of the azachalcone pi-system. The molecular structure was topologically analyzed within the framework of the quantum theory of atoms in molecules; pi-stacking and donor-acceptor pi contacts are involved in the crystal packing of (E)-3-(9H-fluoren-2-yl)-1-(pyridin-2-yl)prop-2-en-1-one (3). (c) 2015 Elsevier B.V. All rights reserved.