Mass spectrometry in structural and stereochemical problems. 2617—The effect of stereochemistry on the course of the characteristic ring D fragmentation of steroid hydrocarbons

The ring D cleavage of the sterol skeleton with loss of carbon atoms 15, 16 and 17 together with the side‐chain is one of the most characteristic and structurally useful mass spectral features of steroids. It has been tacitly assumed that the hydrogen rearrangements accompanying this process are not sensitive to stereochemical changes. Using deuterium labeling it has now been demonstrated that the stereochemistry at various positions of the nucleus, notably 8, 9 and 14, strongly affects this process. Possible rationalizations for this unexpected observation are presented.