Vibrational assignments of 2-iodopyridine

A review of the vibrational assignments for 2-iodopyridine has been proposed based on the FT-Raman (3500-50 cm−1) and IR (4000-400 cm−1) spectral measurements. Equilibrium geometries and vibrational frequencies have been computed from a variety of electronic structure methods: the ab initio (RHF), six DFT (BLYP, BP86, B3LYP, B3P86, B3PW91 and SVWN) and MP2 methods using 3-21G*, LANL2DZ and DGDZVP basis sets. A normal coordinate analysis has been carried out: the normal modes and their couplings are characterized in terms of potential energy distributions (PEDs). The comparison of assignments for pyridine and halopyridines shows that several of the normal modes arise from coupled vibrations in 2-iodopyridine. The BP86 and B3LYP methods with LANL2DZ basis set have performed reasonably well in reproducing the observed spectra, demonstrating that the LANL2DZ basis set (with effective core potential representations of electrons near the nuclei for post-third row atoms) is suitable for 2-iodopyridine.