The 1,3-intramolecular hydrogen transfer in the HSCH(O) reversible arrow (S)CHOH and HSNO reversible arrow SNOH reactions is studied through density functional theory calculations. The reaction force together with structural and electronic properties is monitored along the reaction path to characterize the mechanism of hydrogen transfer. It is found that in both reactions the hydrogen transfer is activated by the structural rearrangement of the backbone atoms that allow the electrostatic interactions to promote the hydrogen transfer in a stepwise mechanism.