A computational study of the nuclear magnetic resonance parameters for double proton exchange pathways in the formamide–formic acid and formamide–formamidine complexes

Abstract

In this paper, we present density functional theory calculations to predict the NMR parameters for two model systems: the formamide-formic acid (FM...FA) and formamide-formamidine (FM...FI) complexes, where intermolecular double proton exchange occurs. For the first time, the NMR parameters have been calculated along the reaction paths of the proton transfers described by means of the intrinsic reaction coordinate (IRC) procedure. The most interesting one-bond spin-spin coupling constants, (1(h))J(XH), between migrating protons and heavier nuclei change character from intra- to intermolecular along the pathway. The maximal positive values of the reduced (1(h))K(XH) coupling constants correspond to the situation when they are intramolecular; they decrease along the path, change sign and reach small negative values, becoming intermolecular couplings. The differing character of the double proton exchange resulting from the synchronicity or asynchronicity of the process is reflected in the calculated NMR parameters. Surprisingly substantial values have been calculated for the six-bond intermolecular proton-proton (6h)J(HH) coupling constants between protons bound to the carbon atoms. A simple procedure consisting of removal of the proton(s) forming the hydrogen bonds has been employed to indicate an influence of hydrogen bonding on the intermolecular coupling constants. Some of the spin-spin coupling constants ((2h)J(XY)) are predominantly transmitted through hydrogen bonds and decrease with removal of the proton(s), while others ((4h)J(CC)) are less sensitive to the presence or absence of the protons of hydrogen bonding.

Prediction and characterization of halogen bonds involving formamidine and its derivatives

“…1), it is concluded that the imino nitrogen atom of FA-(Z) is a better proton acceptor in hydrogen bonding than that of FA-(E). However, the E conformation is often found to participate in hydrogen bonds [17][18][19][20][21][22][23][24][25][26]. This is due to the fact that the E isomer of FA which can be explained with the anisotropic distribution of electrostatic potentials on the halogen atomic surface [39].…”

“…Also it has been established that amidines can form strong hydrogen-bonded complexes with itself [17,18], formic acid [19][20][21], formamide [22,23], glycinamide [24], water [21,25], and alcohols [26]. In the study of these hydrogen-bonded complexes, much attention has been paid to proton transfer, particularly multiproton transfer, because it plays an important role in the proton relay occurring in enzymatic reactions, transport phenomena in biological membrane, and DNA mutations.…”

Abnormal Tetrel Bonds between Formamidine and TH3F: Substituent Effects

“…They are often used as organosuperbases with strong basicity due to the resonance effect . For example, they form strong hydrogen‐ and halogen‐bonded complexes. Interestingly, these strong hydrogen bonds cause proton transfer, which is crucial in enzymatic reactions, transport phenomena in biological membranes and DNA mutations.…”

“…[39] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 are often used as organosuperbases with strong basicity due to the resonance effect. [40] For example, they form strong hydrogen- [41][42][43] and halogen-bonded [44] complexes. Interestingly, these strong hydrogen bonds cause proton transfer, which is crucial in enzymatic reactions, transport phenomena in biological membranes and DNA mutations.…”

Hydrogen bond and the resonance effect on the formamide–water complexes

“…Given the relevance of electronic effects in amides, coupled to hydrogen bonding importance 52–59, as well as the understanding of its effects on the electronic delocalization 10, 57, 60, it is worthwhile to investigate the electronic effects present in formamide–water complexes. The complexes have been studied by means of the natural bond orbitals (NBO) and NRT methods.…”