Influence of an Oriented External Electric Field on the Mechanism of Double Proton Transfer between Pyrazole and Guanidine: from an Asynchronous Plateau Transition State to a Synchronous or Stepwise Mechanism

Abstract

The double proton transfer (DPT) reaction between pyrazole and guanidine, a concerted reaction but strongly asynchronous and presenting a “plateau transition region”, has been theoretically reinvestigated in the presence of an external uniform electric field. First, we computed the reaction path by DFT and proposed a very detailed description of the constitutive electronic events, based on the ELF topology and the bond evolution theory. Then, we studied the effect of an oriented external electric field (OEEF) on the reaction mechanism, for an OEEF oriented along the proton transfer axis. We observe that in one direction, the DPT reaction can be transformed into a stepwise reaction, going through a stabilized single proton transferred intermediate. Contrarily, the two proton transfers occur simultaneously when the electric field is applied in the opposite direction. In the latter case, the order in which the two protons are transferred in the same elementary step can even be reversed if the OEEF is intense enough. Finally, it has been shown that the evolution of the double proton transfer reaction in the presence of an electric field could be quantitatively anticipated by analyzing the ELF value at the bifurcation point between V­(A, H) proton donor and V­(B) proton acceptor of the double hydrogen bonded complex in the entrance channel.

A catastrophe theory-based model for optimal control of chemical reactions by means of oriented electric fields

“…These experiments have motivated new computational studies aimed at understanding and predicting the influence of OEEFs on reactivity [16][17][18][19][20]. These studies have demonstrated that OEEFs can accelerate many types of processes, such as cycloaddition reactions [21][22][23][24][25], the Menshutkin reaction [26], ring opening reactions [27], electrophilic aromatic substitutions [28], oxidative addition reactions between palladium catalysts and alkyl/aryl electrophiles [29], the Kemp elimination reaction [30], degradation of bromobenzene [31], CH 4 oxidation [32], processes in heterogeneous catalysis [33,34], isomerizations [35], conformational rearrangements [36], proton transfers [37,38]. In parallel to all these efforts, the impact of electric fields in the active sites of enzymes on biochemical processes has also received a great deal of attention in recent years [39][40][41][42][43][44][45][46][47].…”

Oriented External Electric Field Modulated Superhalogen Characteristic and Photoelectric Properties of Al4N2 Cluster: A Density Functional Theory Study

“…Conversely, when an electric field is applied in the opposite direction, the two proton transfers occur simultaneously. [42] Based on these facts, although the OEEF has been studied extensively in its role of maintaining the properties of small molecules and controlling chemical activity, research on its effect on metal clusters remains limited. Therefore, herein, we are interested in whether the OEEF can modulate the electronic properties, NLO responses and superhalogen characteristics of main group metal-doped clusters.…”

“…This transformation involves the formation of a stabilized intermediate through the transfer of a single proton. Conversely, when an electric field is applied in the opposite direction, the two proton transfers occur simultaneously [42] …”

“…[21][22][23] Over the last two decades, the oriented external electric field (OEEF) has been extensively implemented as an efficient method for modifying various species' properties, including their geometrical and electronic structures, dipole moment, reactivity, and NLO etc. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Mata et al conducted DFT calculations to examine the hydrogen bond interaction energy of HFÀ HR (R = H, Li, Al, Cl, CCH) complexes under external electric fields. [28] Trusso and colleagues conducted a thorough study on the impact of OEEF on the dipole moment and IR spectrum of the nonpolar centrosymmetric indigo molecule.…”

“…Over the last two decades, the oriented external electric field (OEEF) has been extensively implemented as an efficient method for modifying various species’ properties, including their geometrical and electronic structures, dipole moment, reactivity, and NLO etc [24–43] . Mata et al .…”