The conformation of non-aromatic ring compounds—XL: Characteristic vibration frequencies of some cyclic vicinal dihalogenides with anti configuration—I.

Abstract

A study of the infrared and Raman spectra of vicinal dihalogenides with anti (diaxial) orientation in the cyclohexane, -pentane, dioxane, tetrahydropyran and steroid series reveals that the two CHal stretching frequencies occur characteristically as a strongly coupled pair: an intense Raman band (ν s) and a strong infrared active mode of vibration at lower frequency (ν as). The position of the bands and the difference ν s-ν as are functions of the structure in the vicinity of the CHal bond, the CCl stretching frequencies being sensitive to structural variations more than the CBr frequencies. In mixed dihalides (bromo-chlorides) the stretching modes are also strongly coupled. Frequency ranges of sec—sec and sec—tert dihalides are given. The CHal stretching frequencies of the diequatorial conformations are weakly coupled. It is shown that a relatively small set of empirically determined values suffices to predict with fair accuracy the frequencies, or, in coupled systems, the average frequency, displayed by vic dichlorides and dibromides.