Abstract
The geometry of anthrone and anthraquinone—natural substances of plant origin—was investigated under the substitution of hydrogen atoms in side aromatic ring and, for anthrone, also in the central ring. A significant influence of substitution on geometry expressed by the angle between the side rings was shown. The geometry changes are connected with the changes of electron density and aromaticity of the anthrone and anthraquinone rings. The flexibility of the investigated compounds was confirmed by comparison of the optimized molecules and the molecules in the crystal state where the packing forces can influence the molecular geometry.
Highlights
Anthrones are compounds of natural origin extracted from plants
In the frame of quantum theory of atoms in molecules (QTAIM), the molecule is treated as electron density, $(r), characterized by a system of critical points (CP) for which anthracene-9,10-dione the gradient of the electron density0.003 vanishes
It has been shown that the parameters used in the QTAIM theory to describe the electron density, such as electron density and potential and kinetic energy at the critical point of the ring, can be used as parameters describing the aromaticity of the ring [38]
Summary
Anthrones are compounds of natural origin extracted from plants. The broad specAnthrones are compounds of natural origin extracted from plants. High π-electron delocalization in the condensed rings suggests that the central ring in anthrone and anthraquinone may change aromaticity under the influence of electron density change in the molecule caused by the presence of substituents. Because it can be expected that a substituent attached to the aromatic ring can affect the geometry of the investigated molecules, a systematic study of the structural parameters under substitution was performed. To investigate the influence of substitution on the geometry of the anthrone, the structures with NO2 , CHO, COOH, CH3 , CH2 CH3 , NH2 , OH, Cl, and C(CH3 ) substituents in the central ring were optimized. The structures of anthrones and anthraquinones with electron-donor and electron-withdrawing substituents at the aromatic side ring were optimized (Scheme 3). The wave function evaluated for the optimized molecules was used as the input to the AIMALL program [21]
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