Following the observation that the m/z 101 peak is usually the base peak in the electron ionization mass spectra of di-O-isopropylidenated aldohexofuranose derivatives, quantum chemical calculations were carried out in order to provide a judicious explanation for the preference of these derivatives towards the cleavage of the exocyclic dioxolane moiety. It was also established that geminal electron donor functional groups play an important part in the stabilization of the radical cation generated during the loss of one electron from these compounds (the ionization process). In this paper, by using the PM7 semi-empirical method we show that the radical character is preferentially located between the C4-C5 carbon atoms from the di-O-isopropylidenated derivatives, which is why the C4-C5 bond becomes elongated, thus justifying the cleavage that produces the high intensity peak at m/z 101
