Crystal structure and feasibility of intramolecular proton transfer reaction of salicylaldazine

Abstract

The work describes characterization of salicylaldazine by IR, NMR and single crystal X-ray diffraction studies. The compound crystallizes in the monoclinic crystal system with the space group P2 1/ n, a=8.554(3), b=6.338(2), c=11.864(5) Å, and β=107.89(2)°. There are two strong intramolecular hydrogen bonds of the type O–H⋯N and two weak hydrogen bridges of the type C–H⋯O which help the molecules to pack in a layered structure. Semi-empirical calculations have been performed to predict theoretically the feasibility of intramolecular ground and/or excited state proton transfer reaction/s. Potential energy curves have been generated in the ground (S 0) and the lowest excited (S 1) singlet states to judge the feasibility of intramolecular single and double proton transfer reactions. Semi-empirical (AM1) calculations suggest that only the excited state intramolecular single proton transfer process is favored both thermodynamically and kinetically. No other prototropic processes are theoretically feasible.