Crystal structure and feasibility of intramolecular proton transfer reaction of salicylaldazine

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 P21=n; a ¼ 8:554ð3Þ, b ¼ 6:338ð2Þ, c ¼ 11:864ð5Þ A ° , and b ¼ 107:89ð2Þ8: 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 (S0) and the lowest excited (S1) 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. q 2004 Elsevier B.V. All rights reserved.