67 research outputs found
Why 1,2‑quinone derivatives are more stable than their 2,3‑analogues?
In this work, we have studied the relative stability
of 1,2- and 2,3-quinones. While 1,2-quinones have
a closed-shell singlet ground state, the ground state for
the studied 2,3-isomers is open-shell singlet, except for
2,3-naphthaquinone that has a closed-shell singlet ground
state. In all cases, 1,2-quinones are more stable than their
2,3-counterparts. We analyzed the reasons for the higher
stability of the 1,2-isomers through energy decomposition
analysis in the framework of Kohn–Sham molecular orbital
theory. The results showed that we have to trace the origin
of 1,2-quinones’ enhanced stability to the more efficient
bonding in the π-electron system due to more favorable
overlap between the SOMOπ of the ·C4n−2H2n–CH·· and
··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore,
whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric,
energetic, and electronic), 2,3-quinone derivatives present a
substantial breaking in monotonicity.European
Union in the framework of European Social Fund through the Warsaw
University of Technology Development Programme. O.A. S., H.
S. and T.M. K
Electron-topological, energetic and π-electron delocalization analysis of ketoenamine-enolimine tautomeric equilibrium
The ketoenamine-enolimine tautometic equilibrium has been studied by the analysis of aromaticity and electron-topological parameters. The influence of substituents on the energy of the transition state and of the tautomeric forms has been investigated for different positions of chelate chain. The quantum theory of atoms in molecules method (QTAIM) has been applied to study changes in the electron-topological parameters of the molecule with respect to the tautomeric equilibrium in intramolecular hydrogen bond. Dependencies of the HOMA aromaticity index and electron density at the critical points defining aromaticity and electronic state of the chelate chain on the transition state (TS), OH and HN tautomeric forms have been obtained
Temperature-dependent polymorphism of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide: experimental and theoretical studies on intermolecular interactions in the crystal state
X-ray analysis of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide reveals the temperature-dependent polymorphism associated with the crystallographic symmetry conversion. The observed crystal structure transformation corresponds to a symmetry reduction from I41 /a (I) to P43 (II) space groups. The phase transition mainly concerns the subtle but clearly noticeable reorganization of molecules in the crystal space, with the structure of individual molecules left almost unchanged. The Hirshfeld surface analysis shows that various intermolecular contacts play an important role in the crystal packing, revealing graphically the differences in spatial arrangements of the molecules in both polymorphs. The N-oxide oxygen atom acts as a formally negatively charged hydrogen bonding acceptor in intramolecular hydrogen bond of N–H…O− type. The combined crystallographic and theoretical DFT methods demonstrate that the observed intramolecular N-oxide N–H…O hydrogen bond should be classified as a very strong charge-assisted and closed-shell non-covalent interaction
π-Electronic Communication through Mono- and Multinuclear Gold(I) Complexes
We have theoretically studied gold(I) complexes of the type
The use of topological analysis of electron density in characterization of noncovalent interactions
All atomic and molecular properties are governed by an electron density distribution.
Thus, the methods that deal with an analysis of the electron density distribution
should have a particular appeal for chemists and help to understand the electron
structure of molecules. The Quantum Theory of Atoms in Molecules gives the
unique opportunity to have an insight into a region (e.g., an atom) of a given system
(e.g. a molecule), delivering partitioning scheme which is defined explicitly within
the rigorous quantum theory, from one side, and is applicable for experimentally
available set of observables, from the other side. In that way QTAIM delivers a chemist
a theoretical tool to study a small part of a molecule only, instead of dealing with
the total energy of a whole system. In consequence, QTAIM has become one of the
most powerful utilities of modern chemistry, forming a bridge between advanced
theoretical and experimental techniques. In particular the properties of the electron
density function in the so-called bond critical point (BCP, the (3, -1) saddle point
on electron density curvature) seem to be valuable information for chemists, since
it was proven in many papers that the chemical bonding can be characterized and
classified on the basis of electron density characteristics measured in BCPs .
In this review we firstly give a brief introduction to the theory, explaining most
basic terms and dependences. In the main part of the review we discuss application
of QTAIM in the qualitative and quantitative analysis of several various noncovalent
interactions, focusing readers attention on such aspects as classification of interactions
and interaction energy assessment. Both theoretical and experimental approaches
are taken into account. We also discuss extensions of QTAIM to the analysis of
the so called source function – the method which additionally enlarge interpretative
possibilities of its parent theory.
Finally, we give some examples which perhaps escape a rigorous QTAIM definition
of chemical bonding. We acquaint the potential reader with arguments being
pro- and against the QTAIM-based deterministic model of a chemical bond
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