Apicophilicity versus Hydrogen Bonding. Intramolecular Coordination and Hydrogen Bonds in N-[(Hydroxydimethylsilyl)methyl]-N,N′-propyleneurea and Its Hydrochloride. DFT and FT-IR Study and QTAIM and NBO Analysis

Abstract

Conformers of N-[(hydroxydimethylsilyl)methyl]-N,N′-propyleneurea (1) and their hydrochlorides (2) with HCl coordinated to different basic sites have been studied experimentally by FT-IR and theoretically using the density functional theory (DFT) method at the B3LYP/6-311+G(d,p) and M06/6-311+G(d,p) levels of theory. The structures of silanols 1 and 2 are determined by the balance of two competing effects: namely, intramolecular CO→Si coordination and intramolecular C OThe preferred conformation of silanol 1 is that with an equatorial hydroxyl group, in apparent contradiction with the apicophilicity rule. In the crystal, silanol 1 exists as a conformer with a bifurcated bond composed of a weak CO→Si coordinated bond and a substantially more strong CO•••H−O hydrogen bond. From the NBO analysis, the energies of the n O → σ* Si−X and n O → σ* H−O orbital interactions responsible for the formation of the coordination and hydrogen bonds, as well as the lengths of these bonds, change in opposite directions. In solution the equilibrium is shifted toward the conformer having only the hydrogen bond and no coordination bond. Its hydrochloride 2 exists in the crystal as a conformer with the axial OH group coordinated to HCl, whereas in solution it appears to be in equilibrium with a conformer having the equatorial OH group, in which a four-centered bifurcated bond is formed by two intramolecular components CO→Si and CO•••HO and one intermolecular component CO•••HCl. The QTAIM analysis showed the O→Si coordination bonds in the studied compounds to fall in the range from partially covalent and weak donor−acceptor to mainly electrostatic in nature and the hydrogen bonds to vary from weak to medium in energy.

Effect of proton donors on the intramolecular coordination C=O→Si-F in (acyloxymethyl)trifluorosilanes.Ab initio,DFT and FTIR study, QTAIM analysis

“…The calculated topological parameters of the BCPs and calculated QTAIM energies of intramolecular coordination and intermolecular hydrogen bonds have shown that the C=O→Si bonds are relatively strong and contain covalent contribution, whereas weak hydrogen bonds are electrostatic in nature. This is their distinction from silanols, in which the energy of the C=O→Si intramolecular coordination bonds and of hydrogen bonds C=O···HO may be comparable and dependent both on the axial substituent at silicon and the center of basicity in the molecule to which the HCl molecule is coordinated . The energy of the C=O→Si bond in H‐complexes of conformer 1a exponentially depends on the interatomic distance O→Si.…”

“…Recently we have shown that N ‐[hydroxy(dimethyl)silylmethyl]‐ N,N′ ‐propylene urea can form two types of intramolecular bonds: coordination bond C=O→Si and hydrogen bond C=O···H–O. In its hydrochloride, the strength of the C=O→Si bond depends on to which center of basicity in the molecule is the molecule of HCl bound . In continuation of this study we present here the results of experimental and theoretical investigation of the interaction of (acyloxymethyl)trifluorosilanes RC(O)OCH 2 SiF 3 having the intramolecular coordination bond C=O→Si–F, with proton donors.…”

“…In its hydrochloride, the strength of the C=O→Si bond depends on to which center of basicity in the molecule is the molecule of HCl bound. [45] In continuation of this study we present here the results of experimental and theoretical investigation of the interaction of (acyloxymethyl)trifluorosilanes RC(O)OCH 2 SiF 3 having the intramolecular coordination bond C=O→Si-F, with proton donors. The carbonyl oxygen and the axial fluorine atom involved in the formation of this three-centered four-electron bond are basic centers of the molecule.…”

Influence of electron acceptors on the kinetics of metoprolol photocatalytic degradation in TiO2 suspension. A combined experimental and theoretical study

“…11,12,[53][54][55][56] The significance of the chemical or physical interactions between MET and radical species can be assessed by using the total sum of the delocalization energies, ΣE (2), obtained by summing the electron delocalization energies of all the significant interactions between the NBO orbitals of interacting molecules. 57,58 The ΣE (2) values are reported in Table 3.…”

“…9 Additional oxidants, such as H 2 O 2 , By employing computer simulations within the framework of the density functional theory (DFT), it is possible to gain insight into the changes of the investigated structures as a consequence of the presence of other molecules in the system. 11,12 The information thus obtained is very important to further understand the degradation mechanisms of the investigated compounds. 13,14 Fukui functions and Fukui indices are often used as local quantum-molecular descriptors.…”