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1.
Scheme 1

Scheme 1. From: Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms.

Isomerisation of bicyclo[2.2.0]hexa-1,3-diene, Dewar benzene (1), to benzene (2) and of 2-aza-3-borabicyclo[2.2.0]hex-5-ene (3) to 1,2-dihydro-1,2-azaborine (4).

Holger F Bettinger, et al. Beilstein J Org Chem. 2013;9:761-766.

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2.
Fig. 3

Fig. 3. Fluorobenzene transforming into fluor Dewar benzene.. From: Synchronizing chemistry, quantum mechanics and radioactivity in a revolutionary renewed atom model. Part 1: the elements where Z is 1–10 (H, He, Li, Be, B, C, N, O, F, Ne).

Gerard W. M. Visser, et al. RSC Adv. 2021 Aug 16;11(45):27978-27991.

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3.
Fig. 5

Fig. 5. Stationary points identified on S0 by the NANR; fulvene and Dewar benzene were not discovered by the nanoreactor, and are added for comparison. All energies are referenced to the S0 equilibrium geometry of benzene at their respective level of theory.. From: The non-adiabatic nanoreactor: towards the automated discovery of photochemistry.

Elisa Pieri, et al. Chem Sci. 2021 Jun 2;12(21):7294-7307.

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4.
Fig. 1

Fig. 1. Mechanical activation pathways of the investigated mechanophores (a: Dewar benzene, b: benzocyclobutene, c: gem-dichlorocyclopropane) and investigated linkers.. From: The activation efficiency of mechanophores can be modulated by adjacent polymer composition.

Sourabh Kumar, et al. RSC Adv. 2021 Feb 10;11(13):7391-7396.

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5.
Scheme 4

Scheme 4. From: Valence Bond Theory—Its Birth, Struggles with Molecular Orbital Theory, Its Present State and Future Prospects.

The VB structures (Rumer structures) for describing the π-electronic system of benzene; two Kekulé structures (K1 and K2) and three Dewar Structures (D1–D3). K1 + K2 dominate the wave function.

Sason Shaik, et al. Molecules. 2021 Mar;26(6):1624.

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6.
Fig. 3

Fig. 3. Dewar benzene with an amide linker with bond angle nomenclature (a). Progression of bond angles β0 (b), β1 (c) and β2 (d) with external stretching force.. From: The activation efficiency of mechanophores can be modulated by adjacent polymer composition.

Sourabh Kumar, et al. RSC Adv. 2021 Feb 10;11(13):7391-7396.

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7.
Fig. 2

Fig. 2. Rupture forces for the mechanical activation of Dewar benzene, benzocyclobutene and gem-dichlorocyclopropane using different linkers that connect the mechanophores to the rest of the polymer backbone. Color code: gray: carbon; red: oxygen; blue: nitrogen; white: hydrogen.. From: The activation efficiency of mechanophores can be modulated by adjacent polymer composition.

Sourabh Kumar, et al. RSC Adv. 2021 Feb 10;11(13):7391-7396.

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8.
Fig. 1

Fig. 1. Molecular structures of (4n + 2) (n = 1) π-aromatic heterocycles: The diphosphatriazolate anion (P2N3−, 1) and cyclotriphosphazene (P3N3, 2) along with their isovalent cyclopentadienyl (C5H5−, 3) and benzene (C6H6, 4) counterparts.. From: The elusive cyclotriphosphazene molecule and its Dewar benzene–type valence isomer (P3N3).

The Dewar benzene–type molecular structures of the valence isomers 1,3,5-triphosha-2,4,6-triazabicyclo[2.2.0]hexa-2,5-diene (5) and bicycle [2.2.0]hexa-2,5-diene (6) are also shown. The atoms are color coded in black (carbon), white (hydrogen), blue (nitrogen), and orange (phosphorous).

Cheng Zhu, et al. Sci Adv. 2020 Jul;6(30):eaba6934.

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9.
Scheme 96

Scheme 96. From: Selected synthetic strategies to cyclophanes.

Synthesis of the [6]paracyclophane via isomerization of Dewar benzene. Reagents and conditions: (i) methyl acrylate, ether, 500 W, 3–5 h, 49%; (ii) HCO2Me, MeONa, TsN3, hv, MeOH, 2 h, 35%; (iii) LDA, THF, −78 °C, Ph2Se2, HMPA, 1 h, 32%; (iv) pyridine, CH2Cl2, H2O2, 1.5 h, 40 °C, 73%; (v) C6H6, 50 °C, 95 h, 90%.

Sambasivarao Kotha, et al. Beilstein J Org Chem. 2015;11:1274-1331.

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10.
Fig. 5

Fig. 5. Homodesmotic equations (I to III) for the determination of the aromatic stabilization of benzene (4), borazine (15), and cyclotriphosphazene (2) and computed NICS values (given in parts per million, ppm) at the B3LYP/cc-pVTZ level of theory.. From: The elusive cyclotriphosphazene molecule and its Dewar benzene–type valence isomer (P3N3).

Cheng Zhu, et al. Sci Adv. 2020 Jul;6(30):eaba6934.

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11.
Fig. 1

Fig. 1. The use of the isomer counting method was key to the 19th century assignment of the Kekulé structure to benzene. Dewar benzene and Ladenburg's prismane structures were abandoned. Isomer counting for aromatic systems was used as late as 1914. See text for additional details. The arguments get complicated when considering the isomers shown in the hypothetical eqn (1); exceptionally fast rates of interconversion of these postulated isomers would account for only a single isolated o-xylene. Ultimately, quantum chemistry came to the rescue. The molecular orbital description explored fully by Hückel in the 1930s and the valence bond description using resonance theory by Pauling and Wheland in 1933 were ultimately demonstrated to be equivalent by Shaik and Hiberty. Though it was not emphasized at the time, the logic of isomer counting is equivalent to symmetry arguments. See discussion about “unforeseeable knowledge” in Section 7.. From: Understanding chemistry: from “heuristic (soft) explanations and reasoning by analogy” to “quantum chemistry”.

Jeffrey I. Seeman, et al. Chem Sci. 2022 Oct 12;13(39):11461-11486.

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