Structure, energy, vibrational spectrum, and Bader's analysis of π⋯H hydrogen bonds and H^−δ⋯H^+δdihydrogen bonds

Abstract

In this paper, the intermolecular structural study asserted by the vibrational analysis in the stretch frequencies of hydrogen bonds (π···H) and dihydrogen bonds (H(-δ)···H(+δ)) have definitively been revisited by means of calculations carried out by Density Functional Theory (DFT) and topological parameters derived from the classic treatise of the Quantum Theory of Atoms in Molecules (QTAIM). As a matter of fact the π···H hydrogen bond is formed between the hydrofluoric acid and the C≡C bond of the acetylene, but the QTAIM calculations revealed a distortion in this interaction due to the formation of the ternary complex C(2)H(2)···2(HF). Although the π bonds of ethylene (C(2)H(4)), propylene (C(2)H(3)(CH(3))), and t-butylene (C(2)H(2)(CH(3))(2)) are considered proton acceptors, two hydrogen-bond types--π···H and C···H--can be observed. Over and above the analysis of the π hydrogen bonds, theoretical arguments also were used to discuss the red-shifts in the stretch frequencies of the binary dihydrogen complexes formed by BeH(2)···HX with X = F, Cl, CN, and CCH. Although a vibrational blue-shift in the stretch frequency of the H-C bond of HCF(3) due to the formation of the BeH(2)···HCF(3) dihydrogen complex was obtained, unmistakable red-shifts were detected in LiH···HCF(3), MgH(2)···HCF(3), and NaH···HCF(3). Moreover, the alkali-halogen bonds were identified in relation to the formation of the trimolecular systems NaH···2(HCF(3)) and NaH···2(HCCl(3)). At last, theoretical calculations and QTAIM molecular integrations were used to study a novel class of dihydrogen-bonded complexes (mC(2)H(5)(+)···nMgH(2) with m = 1 or 2 and n = 1 or 2) based in the insight that MgH(2) can bind with the non-localized hydrogen H(+δ) of the ethyl cation (C(2)H(5)(+)). In an overview, QTAIM calculations were applied to evaluate the molecular topography, charge density, as well as to interpret the shifted frequencies either to red or blue caused by the formation of the hydrogen bonds and dihydrogen bonds.

Comparisons between Crystallography Data and Theoretical Parameters and the Formation of Intramolecular Hydrogen Bonds: Benznidazole

“…According to values of 0.733 and 0.738 gathered in Table 3, the C-H c •••O b =N intramolecular hydrogen bonds behave with a trend of covalence in 1K and 1W, although the electronic density values are not the largest, and the bond lengths are not the shortedones, as demonstrated in Figure 7. This can be stated once these results are smaller than 1.0 [32,58]. In regards to the remaining hydrogen bonds, all of them are non-covalent.…”

“…In this sense, we are convinced that QTAIM can be decisive in our investigation not only regarding the intramolecular hydrogen bonds [23][24][25][26][27][28][29][30][31], but also to unveil the most stable conformation of benznidazole. Another interesting viewpoint is that the solvent effect may be responsible for drastic changes in several molecular properties, e.g., geometrical deformations; increase in the reaction rate; control of products along the reaction paths, for instance [32][33]. If we consider that intramolecular hydrogen bonds can be formed in the minimum structure of benznidazole, the specialized literature informs us that the application of the Polarized Continuum Model (PCM) [34] to evaluate the solvent effect is recommended [35][36][37][38][39].…”

“…Regarding the interaction strength, the −G/U ratio is a qualitative manner to express the appearing of covalent effect [32]. According to values of 0.733 and 0.738 gathered in Table 3, the C-H c •••O b =N intramolecular hydrogen bonds behave with a trend of covalence in 1K and 1W, although the electronic density values are not the largest, and the bond lengths are not the shortedones, as demonstrated in Figure 7.…”

O paradigma da estrutura do doador de próton na formação de ligações de hidrogênio: complexo C2H2∙∙∙6(HF)

“…[7][8][9][10] Entretanto, sabe-se que a densidade eletrônica é uma propriedade cooperativa, 11 e centros incipientes de elétrons também podem interagir com espécies ácidas, em outras palavras as nuvens eletrônicas das ligações p de hidrocarboneto. [12][13][14] Neste contexto, foi demonstrado que o acetileno e anteriormente o etileno possuem a capacidade de interagir com ácido fluorídrico e formarem complexos de hidrogênio [17][18] mas no entanto, recentemente alguns estudos têm sido feitos com o propósito de definir o poder eletrônico da ligação p em transferir carga para o orbital LUMO de espécies ácidas, 19 além de ácido fluorídrico, mas também do ácido clorídrico. 12,[20][21] Foram reportadas as propriedades estruturais, eletrônicas e vibracionais dos complexos de hidrogênio C 2 H 2 •••n(HF) e C 2 H 4 •••m(HF) para n = 2 e 4 e m = 2.…”

“…[12][13][14] Neste contexto, foi demonstrado que o acetileno e anteriormente o etileno possuem a capacidade de interagir com ácido fluorídrico e formarem complexos de hidrogênio [17][18] mas no entanto, recentemente alguns estudos têm sido feitos com o propósito de definir o poder eletrônico da ligação p em transferir carga para o orbital LUMO de espécies ácidas, 19 além de ácido fluorídrico, mas também do ácido clorídrico. 12,[20][21] Foram reportadas as propriedades estruturais, eletrônicas e vibracionais dos complexos de hidrogênio C 2 H 2 •••n(HF) e C 2 H 4 •••m(HF) para n = 2 e 4 e m = 2. 22 Os resultados apontam para o comprometimento da integridade da ligação de hidrogênio p•••H, em que surge uma nova interação, a C•••H.…”