Conformation of open‐chain compounds. Part 3. Carbon‐halogen stretching frequencies and conformation of some vicinal dihalides

Abstract

AbstractA study of the infrared and Raman spectra of some vicinal dihalogeno‐ethanes, ‐propanes and ‐butanes with predominant antiperiplanar orientation in the straight chain and branched series, reveals that the two C‐Hal stretching frequencies occur characteristically as a more or less strongly coupled pair: an intense Raman band (νs) and a strong infrared active mode of vibration (νas) at lower frequencey.The C‐Hal frequencies of the gauche conformations are weakly coupled.The position of the bands and the difference Δν = νs − νas are functions of the chemical/geometrical structure in the vicinity of the C‐Hal bonds. Empirical rules are presented by which the C‐Hal frequencies or, in strongly coupled systems, the average frequency of anti as well as of gauche forms can be predicted with fair accuracy.