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

Abstract

A novel series of pyrrole-2-yl chloromethyl ketones were synthesized and studied by FT-IR, ¹H, ¹³C 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 CO 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 ¹H chemical shift and infrared red shift Δν_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.