Characterizing the Mechanism of the Double Proton Transfer in the Formamide Dimer

Abstract

The double proton transfer in the formamide dimer is characterized computationally by combining density functional theory and ab initio methods. The intrinsic reaction coordinate (IRC) is obtained at the B3LYP level of theory. Energies of several points along the IRC are treated by the more rigorous focal point method to test the validity of the B3LYP functional. The reaction mechanism is examined in terms of the energy profile, the reaction force, the chemical potential, and the reaction electronic flux. The energy profile for the activation process of the formamide dimer to the imino ether product obtained with the B3LYP functional is in agreement with the results of the focal point method. Together with the reaction force analysis and the reaction electronic flux a precise assignment of the structural and electronic contributions to the activation barrier becomes possible. The results show that the reaction starts with a structural rearrangement, where the two dimers approach each other, and is followed by electronic changes before the system reaches the transition state. This electronic contribution to the activation barrier steers the activation process. After the transition state is reached, deviations of the B3LYP functional from the more accurate focal point energies become apparent, where the errors may be rationalized in terms of the treatment of exchange. The inconsistency could be assigned to the incapacity of the functional to describe delocalization effects over the whole system.

Polarization loss in the organic ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA)

“…36,37 Concerted proton transfer has been studied theoretically in formamide dimers, and in those dimers in the gas phase, the proton transfer has a high activation energy of around 42 kJ mol À1 and a low barrier for reversal (6.5 kJ mol À1 ). 38 To investigate the relevance of the proton tunneling scenario outlined above, we prepared deuterated BTA-C10d and BTA-C18d as described in the ESI, † Sections S4-S6. In terms of structural properties and phase behavior the deuterated materials are very similar to the normal protonated materials as is shown in Sections S1 and S3 of the ESI.…”

Revisiting the Rearrangement of Dewar Thiophenes

“…Most reactions encounter a maximum in this path, around which the entire transition state theory has been constructed. One useful tool to dissect the IRC comes from the consideration of the reaction force: [12][13][14]16,17] in conservative systems, the net force acting on the system may be obtained from the derivative of the potential energy:…”

Effects of the ionization in the tautomerism of uracil: A reaction electronic flux perspective

“…The reaction force analysis has been shown to offer interesting insights into many chemical reactions and in particular into hydrogen and proton transfer processes . This formalism is based on the fact that in an elementary reaction, the lowest energy path connecting reactants and products when projected into the intrinsic reaction coordinate (IRC) typically presents a maximum corresponding to the transition state (TS) connecting reactants and products.…”