Revisiting the carbonyl n → π* electronic excitation through topological eyes: expanding, enriching and enhancing the chemical language using electron number distribution functions and domain averaged Fermi holes

Abstract

The theory of chemical bonding is underdeveloped in electronic excited states, even in small molecules. Fortunately, real space tools may be used to offer rich images of simple excitation processes, as is shown in this work. The statistics of electron populations, through a fruitful combination of electron distribution functions (EDFs) and domain averaged Fermi holes (DAFHs), was used to enlighten our chemical knowledge of a paradigmatic process: the n → π* excitation in formaldehyde. Interestingly, our results are perfectly compatible with an alternative perception of the electronic transition: the rotation of one averaged-electron in the oxygen lone pair. This topological model does not require inter-orbital jumps to explain the final electron distribution and, in our humble opinion, this fact makes it, to some extent, more realistic. Finally, other far-reaching conclusions emerge smoothly from our analysis: (i) the σ link may contribute less to the total bond order (as measured by the delocalization index) of a polar double bond than the π one; (ii) populating an antibonding orbital does not necessarily imply decreasing the bond order of its corresponding bond.

Cooperative and anticooperative effects in resonance assisted hydrogen bonds in merged structures of malondialdehyde

“…We can also compare the disminution of the delocalisation in a similar way to equations (21) and (24), Contributions of the intra and interatomic exchange components (in kcal/mol) to ∆E coop (N) with N = 2, 3, or 4 (equation (24)). The values of ∆δ coop (expression (25) in which the primed and unprimed quantities have the same meaning that in equation (24). We observe in Table 5 that the second H-bond in 2 leads to a larger diminution of delocalisation (∆δ coop (2) < 0) in contrast to 3 and 4 (∆δ coop (3) > 0 and ∆δ coop (4) > 0).…”

“…More specifically, we employed the Interacting Quantum Atoms (IQA) energy partition as well as the Quantum Theory of Atoms in Molecules (QTAIM) to analyze the interplay between a given RAHB and its surrounding π bonds as well as the resultant HB cooperative or anticooperative effects. We have chosen these methods of wavefunction analyses for this investigation due to its successful use in the study of different non-additive interactions such as those in H-bond within small water clusters [22,23] , back-bonding in transition metal carbonyl complexes [24,25] , or in n → π transitions in electronic excited states [26] . Altogether, our results provide an assessment of the interaction of an RAHB and its neighboring cojugated system on top of HB π cooperative and anticooperative effects.…”

How Electronic Excitation Can be Used to Inhibit Some Mechanisms Associated to Substituent Effects

“…To this end, we selected the excitation in carbonyl compounds where the conjugation of oxygen with the rest of the molecule is expected to be decoupled. We hope that these results encourage more researchers to take a step in the realm of quantum chemical topology and its possibilities in electronically excited states …”

“…We hope that these results encourage more researcherstotake as tep in the realm of quantum chemical topology [12,13] and its possibilities in electronically excited states. [14][15][16][17][18][19][20][21][22][23][24][25][26]…”