FTIR and Raman spectra and fundamental frequencies of 5-halosubstituted uracils: 5-X-uracil (X = F, Cl, Br and I)

FTIR and Raman spectra of 5-halosubstituted uracils (5-X-uracil; X = F, Cl, Br and I) were recorded in the region 200–4000 cm−1. Assuming under the Cs point group, the distribution of normal mode of vibrations between the two species as planar (a′) and non-planar (a″) are given by 21a′ + 9a″, of which also correspond to the 30 modes of uracil moiety and the electro negativity of halogen group substitution causes some where mixing/shifting in their modes with other modes. The ring breathing and kekule stretching modes are observed in lower magnitudes compared to those of uracil which could be due to mass effect of halogen atom in place of the hydrogen atom. The C–X (X = F, Cl, Br and I) stretching frequency is distinctly separated from the CH/NH ring stretching frequencies on the pyrimidine ring. All other bands have also been assigned different fundamentals/overtones/combinations.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electro negativity of halogen group substitution causes some mixing/shifting with other modes. ► The ring breathing and kekule stretching modes of halo-uracils are observed lower than uracil. ► This could be due to mass effect of halogen atom in place of the hydrogen atom. ► The C–X (X = F, Cl, Br and I) stretching is distinctly separated from the CH/NH stretching frequencies.