Density functional theory study of the substituent effect on the structure, conformation and vibrational spectra in halosubstituted anilines

A comparative density functional theory (DFT) study exploring the structural and spectroscopic properties of the complete set of halosubstituted anilines with the halogens being F, Cl and Br was carried out. This study aims at understanding the effect of the type, number and positions of halogen substituents on the inversion barrier, geometrical properties and vibrational frequencies. The compounds were exclusively predicted to exist in the near-planar pyramidal form. While the order of stability is noted to be independent of the type of halogen substituents, the size of the inversion barrier is predicted to be sensitive to their number and positions, in accordance with former theoretical and experimental reports. The higher number of halogens leads to a more pronounced planarity character of the amino group. The deactivating nature of halogen atoms is believed to enhance the lone-pair electron delocalization in the order of bromo- > chloro- > fluoroanilines. An unusually strong electron delocalization nature is predicted to exist in the case of tetra- and penta-substituted haloanilines.