CONFORMATION OF NON-AROMATIC RING COMPOUNDS .40. CHARACTERISTIC VIBRATION FREQUENCIES OF SOME CYCLIC VICINAL DIHALOGENIDES WITH ANTI CONFIGURATION .I.

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 CHal stretching frequencies occur characteristically as a strongly coupled pair: an intense Raman band (νs) and a strong infrared active mode of vibration at lower frequency (νas). The position of the bands and the difference νs-νas are functions of the structure in the vicinity of the CHal bond, the CCl stretching frequencies being sensitive to structural variations more than the CBr 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 CHal 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. © 1968.