A DFT Study of the Modulation of the Antiaromatic and Open‐Shell Character of Dibenzo[a, f]pentalene by Employing Three Strategies: Additional Benzoannulation, BN/CC Isosterism, and Substitution. Issue 41 (8th July 2019)

• Record Type: Journal Article
• Authors: Baranac‐Stojanović, Marija
• Is Part Of: Chemistry. Volume 25:Issue 41(2019)
• Page Start: 9747
• Page End: 9757
• Publication Date: 2019-07-08
• Subjects: aromaticity -- density functional calculations -- electronic structure -- fused-ring systems -- substituent effects; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201901845
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Dibenzo[ a, f ]pentalene ([ a, f ]DBP ) is a highly antiaromatic molecule having appreciable open‐shell singlet character in its ground state. In this work, DFT calculations at the B3LYP/6‐311+G(d, p) level of theory were performed to explore the efficiency of three strategies, that is, BN/CC isosterism, substitution, and (di)benzoannulation of[ a, f ]DBP, in controlling its electronic state and (anti)aromaticity. To evaluate the type and extent of the latter, the harmonic oscillator model of aromaticity (HOMA) and aromatic fluctuation (FLU) indices were used, along with the nucleus‐independent chemical shift NICS‐XY‐scan procedure. The results suggest that all three strategies could be employed to produce either the closed‐shell system or open‐shell species, which may be in the singlet or triplet ground state. Triplet states have been characterized as aromatic, which is in accordance with Baird's rule. All the singlet states were found to have weaker global paratropicity than[ a, f ]DBP . Additional (di)benzo fusion adds local aromatic subunit(s) and mainly retains the topology of the paratropic ring currents of the basic molecule. The substitution of two carbon atoms by the isoelectronic BN pair, or the introduction of substituents, results either in the same type and very similar topology of ring currents as in the parent compound, or leads to (anti)aromatic and nonaromatic subunits. The triplet states of all the examined compounds are also discussed. Abstract : Taking control ! DFT calculations were performed to explore the efficiency of BN/CC isosterism, substitution, and (di)benzoannulation in controlling the electronic state and (anti)aromaticity of dibenzo[ a, f ]pentalene (see scheme). The results suggest that these two properties can be modulated by applying all three types of modification to the structure of dibenzo[ a, f ]pentalene.