The work dealing with the influence of an Oriented External Electric Field (OEEF) on the reactivity of organic compounds has experienced a resurgence in recent years, particularly because of the prospects offered by this type of external stimulus to control a reaction as “smart reagent”.[1] In this study, we investigated the influence of an OEEF on the double proton transfer mechanism in the pyrazole-guanidine complex. This reaction is concerted in the absence of an OEEF, but its potential energy profile exhibits a broad plateau in the transition state region, suggesting a strongly asynchronous mechanism.[2] This was confirmed by a principal component analysis of the geometry along the reaction coordinate (Figure 1- a), as well as by Born-Oppenheimer molecular dynamics simulations. Evolution of the reaction mechanism as a function of the field direction and strength was studied by DFT (ωB97XD/6-311++G(2d,2p)), complemented by topological analysis of the ELF (electron localization function) along with the reaction coordinate in the context of BET (bonding evolution theory). We show that by applying the OEEF in one direction, it is possible to stabilize a zwitterionic reaction intermediate resulting from a single proton transfer. In the opposite direction, it is possible to synchronize the two proton transfers (Figure 1-b).[3] With NBO calculations and ELF values at the bifurcation point of the hydrogen bonds, we proposed a predictive descriptor of asynchronicity depending on the OEEF intensity. References [1] Stuyver, T.; Danovich, D.; Joy, J.; Shaik, S. WIREs Comput. Mol. Sci. 2020, 10 (2). [2] Schweiger, S.; Rauhut, G. J. Phys. Chem. A 2003, 107 (45), 9668–9678. [3] Geoffroy-Neveux, A.; Labet, V.; Alikhani, M. E. J. Phys. Chem. A 2022, acs.jpca.1c10553