Influence of the O-Protonation in the O═C–O-MeZPreference. A QTAIM Study

Abstract

One of the three O-protonations of methyl formate (MF) gives rise to a system where the Z preference is switched off and the E conformer becomes the most stable arrangement. The quantum theory of atoms in molecules scheme for splitting the physical space of a molecule into atomic subspaces has been employed to analyze this trend, as well as the effect of the protonation in MF. The most important changes in energy and electron density upon protonation do not take place when MF reorganizes its nuclei, but when the proton is introduced explicitly. The same trend is observed when the H attached to the carbonyl C is replaced by electron donating and withdrawing groups (CN, F, OH, CH(3), and CF(3)). The origin of the inversion in the conformational preference relies in the changes experienced by two interactions: (i) the methyl group with the proton and (ii) that between the atoms of the ether C-O bond.

Complexation of common metal cations by cyanins: Binding affinity and molecular structure

“…QTAIM atomic charges of the Cy − ligand become reduced in the complexation process, as exemplified in Figure for OC‐6 [FeCy(H 2 O) 4 ] 2+ and [FeCy 2 (H 2 O) 2 ] + formation (the carbons of the methoxyl groups bonded to C5 and C3, C3’, and C4’ are exceptions to this rule. The reasons for these exceptions can be found considering the same scheme proposed for explaining electron density reorganization in molecular protonations) . Moreover (Tables and ), the results indicate that the larger the net charge transfer (CT), from Cy − to the metal cation, the more favored the metal‐complex formation (the higher binding energy, Δ b E/ Δ b G ).…”

“…[27,28] In the three cases where ρ b values can be compared, that is when an oxidation number differs for the same pair of atoms (Co, Fe and Cr complexes), we observe ( Table 2) The reasons for these exceptions can be found considering the same scheme proposed for explaining electron density reorganization in molecular protonations). [49,50] Moreover (Tables 2 and 4), the results indicate that the larger the net charge transfer (CT), from Cy − to the metal cation, the more favored the metal-complex formation (the higher binding energy, Δ b E/Δ b G). Also, we notice (see Supporting Information Table S4) that coordination number partially modified this trend, as water molecules contribute in reducing the positive charge of the metal and thus, the higher the coordination number the lower CT from Cy − .…”

Excluding hyperconjugation from the Z conformational preference and investigating its origin: formic acid and beyond

“…As we noted in previous studies, [22][23][24] the Z preference is appropriately described at the HF level. This fact can be confirmed by Fig.…”

“…Moreover, during the last few decades, studies carried out with modern electron density analysis methods, which deal with a real observable (electron density), such as the prestigious quantum theory of atoms in molecules (QTAIM), [12][13][14][15] or with methods based on the expansion of the wavefunction in terms of Lewis structures, such as the famous valence bond theory, 16 have given rise to a growing body of evidence that directly questions the reliability of the HM. [17][18][19][20][21][22][23][24][25] Thus, and referring only to conformational preferences, alternative intepretations have been presented for the anomeric effect, [18][19][20][21]24,25 the benzylic effect, 26 and even for the one at issue in this paper: the Z effect. 22 We think it is of importance to revisit the origin of this effect making use of an extensive group of methods included in what is called Quantum Chemical Topology (QCT).…”

Molecular Structure and Internal Rotation of CF3 Group of Methyl Trifluoroacetate: Gas Electron Diffraction, Microwave Spectroscopy, and Quantum Chemical Calculation Studies

“…The anti conformer was also adopted in the interpretation for site-selective dissociation in the total-ion-yield spectrum and time-of-flight mass-spectra of MTFA . The explanation for the anti conformational preference for the ester compounds is based on the hyperconjugative model, but recent quantum chemical studies suggest that the contribution of electron delocalization is less important than other electronic and steric effects. , …”