Vibrational spectra, structure, and theoretical calculations of 2-chloro- and 3-chloropyridine and 2-bromo- and 3-bromopyridine

The infrared and Raman spectra of 2-chloropyridine, 3-chloropyridine, 2-bromopyridine, and 3-bromopyridine have been recorded and assigned. Density functional theory calculations (B3LYP with 6-311++G(d,p) basis set) produce excellent agreement with the experimental values. Ab initio calculations (MP2 with the cc-pVTZ basis set) were utilized to compute the molecular structures, which were compared to those of pyridine and the corresponding fluoropyridines. All of the 2-halopyridines show a shortening of the N–C(2) bond resulting from the halogen substitution on the C(2) carbon atom. All of the other ring bond distances for the 2-halopyridines and 3-halopyridines are little different from pyridine itself.

► The molecular structures of four halopyridines have been calculated.
► The infrared and Raman spectra of these molecules have been recorded and assigned.
► DFT calculations yield excellent agreement with the experimental spectra.
► The nitrogen to carbon bond in the 2-halopyridines is considerably shortened by the halogen substitution.