Theoretical Prediction of Benzyne-Like Species in Pyrene Diradicals

Abstract

The different products that can be obtained from pyrene dehydrogenation have been studied by means of hybrid density functional theory. Most of the didehydrogenated species exhibit a diradical character. This is supported by the closeness between the geometry and energy of singlet and triplet states and the open-shell nature of the singlet state. However, three didehydrogenated species have been found to exhibit a closed-shell singlet electronic ground state. The analysis of the electronic structure, the formation energy of these didehydrogenated species, and their geometrical structure reveals that these three didehydrogenated species are better described as benzyne-like moieties; two of them are of o- and one of m-benzyne character. The two o-benzyne species have lower energies than the m-benzyne and are favored upon diradical formation. This interpretation is fully supported by the analysis of multiconfigurational wave functions and the order of stabilities confirmed by second-order multireference perturbation theory calculations. A possible implication of the reactivity of these benzyne-like species in asphaltene formation is discussed.

Bottom‐Up Synthesis of Advanced Carbonaceous Anode Materials Containing Sulfur for Na‐Ion Batteries

“…[10] Herein, the systematical variation of the C/S ratio enables us to control the interplanar distance (Figure 3a). At low S content (S 0.1-1 Pyr), a peak centered at ≈25.8° corresponding to (002) interplanar stacking was observed, speaking for a less amorphous nature of the material while increasing the molar ratio (S [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Pyr) results in a more amorphous material with a broader peak centered at ≈22.7° ( Figure S4a 20 Pyr, respectively. Both values represent a larger interplanar distance between the layers compared to graphite's (0.335 nm), [11] demonstrating how a controlled S insertion into graphite structure can systematically increase the d 002 .…”

EPR spectroscopic and computational characterization of the 2‐dehydro‐m‐xylylene and 4‐dehydro‐m‐xylylene triradicals

“…In all six systems, rather strong interactions between the in‐plane orbitals (through‐space or through‐bond) lead to low‐spin ground states and comparatively large low‐spin–high‐spin gaps. These interactions are significantly weaker in higher didehydroacenes with a larger separation of the radical sites, which are generally characterized by small singlet–triplet energy splittings . The ground states of these diradicals can often be rationalized by considering the spin polarization of the π‐system .…”

“…These interactions are significantly weaker in higher didehydroacenes with a larger separation of the radical sites, which are generally characterized by small singlet-triplet energy splittings. [31,[35][36][37][38][39] The ground states of these diradicals can often be rationalized by considering the spin polarization of the p-system. [35] In contrast, typical pp and ppp di-and triradicals, such as the non-Kekule hydrocarbon m-xylylene (1,3-quinodimethane) 1 or 1,3,5-trimethylenebenzene 2, show a strong preference for ferromagnetic coupling with robust 3 B 2 and 4 A 2 ground states, respectively, according to their strongly nondisjoint NBMOs (Scheme 1).…”

DFT Molecular Dynamics Study of Pyrene Biradical Species

“…As mentioned before, the geometry optimization process results in a canonical form in which a and d rings (Figure 1) have a localized sextet, respectively; whereas the b and c have double bonds in C4−C5 and C11−C12 (1.363 Å), respectively. Nuclear independent chemical shift analysis gives −14.6 and −6.9 ppm of aromatic character, for the benzenic and nonbenzenic rings, respectively (García-Cruz et al, 2004). This description is completely against the Platt's model because it is impossible to find peripheral aromaticity in a molecule that presents its aromaticity by specific regions (Platt, 1954).…”

“…Lately, García-Cruz et al (2004) have described in detail the electronic structure of pyrene and its radicals, finding a close agreement between x-ray structure and the B3LYP/6-31++G * * optimized geometry of isolated pyrene, providing evidence of the reliability of this level of theory. The pyrene singlet-triplet gap is 48.5 kcal/mol.…”