Mass spectroscopy of natural products. V—Mass spectroscopic studies of ring a substituted allobetulane derivatives

The mass spectrometric behaviour of ring A substituted allobetulane derivatives is discussed. The position and nature of a substituent both influence the mass spectral decomposition remarkably. In the case of the epimeric 1‐hydroxy‐ and acetoxy allobetulanes, the mass spectral differences are great enough to distinguish these from each other. The results should yield a general rationalization for other saturated triterpenes having the same A, B, C ring system.