[en] Collision induced dissociation in mass spectrometry of protonated nucleosides typically yields as charged fragment the protonated nucleobase augmented by one hydrogen transferred from the 2'-deoxyribose, [ bH(2)]. The origin of the hydrogen transfer for the protonated 2'-deoxyguanosine has been investigated by collision induced dissociation of deuterium enriched molecules. [ 1'-H-2] 2'-deoxyguanosine, [ 2',2aEuro(3)-H-2(2)] 2'-deoxyguanosine, and [ 5',5aEuro(3)-H-2(2)] 2'-deoxyguanosine have been studied and deuterium/hydrogen back exchange has been used following complete or partial exchange of the 2'-deoxyguanosine in solution. Based on the fragmentation of the deuterated molecular ions, the hydrogen transferred from the 2'-deoxyribose to the guanine is found to originate from the O5' atom on the 2'-deoxyribose. A fragmentation mechanism involving a hydrogen shift from the 2' position to the oxygen atom O5' and supported by the kinetic isotope effect on the survival yield curves is proposed. The influence of the 2'-deoxyguanosine conformation on the hydrogen transfer and the fragmentation mechanism is discussed.