Predicting an Antiaromatic Benzene Ring in the Ground State Caused by Hyperconjugation

Abstract

Benzene, the prototype of aromatics, has six equivalent C−C bonds (1.397 Å), which are intermediate between a C−C double bond and a C−C single bond. For over 80 years, chemists have spent much effort on freezing a localized structure to obtain a distorted bond‐length alternating benzene ring in the ground state, leading to various localized trisannelated benzene rings. However, most of the central benzene rings are still aromatic or nonaromatic. Here we report an antiaromatic benzene ring caused by hyperconjugation. Specifically, symmetric annulation of 5,5‐difluorocyclopentadiene results in an antiaromatic benzene ring, which is supported by various aromaticity indices, including nucleus‐independent chemical shift, anisotropy of the induced current density, π‐separated electron‐localization function and heat of hydrogenation. Our findings highlight a strong power of hyperconjugation, a “weak” interaction in organic chemistry, paving the way for designing and realizing more novel (anti)aromatics.

Non‐conventional Hydrogen Bonding and Aromaticity: A Systematic Study on Model Nucleobases and Their Solvated Clusters

“…[11] Very recently, analysis of computational C H proton chemical shifts also helped in predicting the antiaromatic character of the benzene ring caused by hyper conjugation. [31] In our case also we computationally observed downfield chemical shift upon H-bonding for all studied complexes of 2PY analogs. To this we also observed a larger magnitude of C H proton chemical shift as we go down the group from 2PY to 2SePY (can be seen in the above table).…”

DNA as a perfect quantum computer based on the quantum physics principles

“…Due to the Molecular Orbital (MO) description of Benzene providing a more satisfying and general treatment of "aromaticity" 53 , 54 , we will first analyze its structure using the oscillatory resonant quantum state between electron and hole pairs. The six-membered ring in Benzene is a perfect hexagon with all Carbon–Carbon bonds having an identical length of 139 pm 55 . All Carbons are hybridized, and have an unhybridized orbital perpendicular to the ring plane 56 .…”

“…The remaining Carbon valence electrons then occupy these molecular orbitals in pairs, resulting in a fully occupied (six electrons) set of bonding molecular orbitals 53 . This closed shell gives the Benzene ring its thermodynamic and chemical stability, just as a filled valence shell octet confers stability on inert gases 55 . We call this common region -MO of Benzene ( -MO B ).…”

DNA as a perfect quantum computer based on the quantum physics principle

“…The sum of the total momentum of the electron and hole pairs is given by: 𝑃 + 𝐾 − 𝑃 = 𝐾 for the electron pairs and −(𝑃 + 𝐾) + 𝑃 = −𝐾 for the hole pairs Due to the Molecular Orbital (MO) description of Benzene providing a more satisfying and general treatment of "aromaticity" 54,55 , we will first analyze its structure using the oscillatory resonant quantum state between electron and hole pairs. The six-membered ring in Benzene is a perfect hexagon with all Carbon-Carbon bonds having an identical length of 139 pm 56 . All Carbons are 𝑠𝑝 2 hybridized, and have an unhybridized 𝑝 𝑧 orbital perpendicular to the ring plane 57 .…”

“…The remaining Carbon valence electrons then occupy these molecular orbitals in pairs, resulting in a fully occupied (six electrons) set of bonding molecular orbitals 54 . This closed shell gives the Benzene ring its thermodynamic and chemical stability, just as a filled valence shell octet confers stability on inert gases 56 . We call this common region 𝜋-MO of Benzene (𝜋-MOB).…”