Normal co-ordinate analysis of 1, 8-dibromooctane

Abstract

The organic compound 1,8-dibromooctane (1,8-DBO) exists in liquid phase at ambient temperatures and has versatile synthetic applications. In its liquid phase 1,8-DBO has been expected to exist in four most probable conformations, with all its carbon atoms in the same plane, having symmetries C 2h , C i , C 2 and C 1. In the present study a detailed vibrational analysis in terms of assignment of Fourier transform infrared (FT-IR) and Raman bands of this molecule using normal co-ordinate calculations has been done. A systematic set of symmetry co-ordinates has been constructed for this molecule and normal co-ordinate analysis is carried out using the computer program MOLVIB. The force-field transferred from already studied lower chain bromo-alkanes is subjected to refinement so as to fit the observed infrared and Raman frequencies with those of calculated ones. The potential energy distribution (PED) has also been calculated for each mode of vibration of the molecule for the assumed conformations.

Vibrational analysis of 1-chlorooctane

“…Normal co-ordinate calculations have been employed in the vibrational spectral analyses of polyatomic molecules during the past few decades [3,4] and now-a-days are commonly used to study complex molecules [5][6][7][8][9][10][11][12]. Experimental considerations alone cannot yield the unique assignment of the observed vibrational frequencies to specific modes of vibration of complex molecules such as 1-CLO.…”

“…The other conformations II, III, and IV as shown in Figures 3(II), (III) and (IV), possess C I symmetry. In the conformation II called gauche, the Cl atom lies above the C-C skeletal plane, while in the conformation III the methyl group attached to the C 7 atom has been rotated about C 6 bond to occupy the position of H 13 . In conformations IV the Cl atom is above (or below) the C-C skeletal plane and the methyl group attached to C 7 is rotated about the C 6 -C 7 bond to occupy the positions of H 13 (or H 14 ).…”