Spectroscopic and theoretical studies on some new pyrrol-2-yl-chloromethyl ketones

A novel series of pyrrole-2-yl chloromethyl ketones were synthesized and studied by FT-IR, H-1, C-13 NMR spectroscopy and DFT calculations at the B3LYP/6-311++G(d,p) level of approximation. Two stable conformations were detected in solution: s-cis and s-trans forms where the C=O group is located on the same side or the opposite side of N-H group, respectively. The conformational stability of these molecules is governed mainly by intermolecular hydrogen bonding interactions. The strength of hydrogen bonds was evaluated on the basis of H-1 chemical shift and infrared red shift Delta nu(N-H) of the stretching vibration of N-H proton donating bonds. The quantum theory of 'atoms in molecules' as well as the natural bond orbital method were applied to characterize hydrogen bonding interactions.