The electronic structure of borabenzene: Combination of an aromatic ?-sextet and a reactive ?-framework

Abstract

ŽThe electronic structure of borabenzene C H B, known also as borinane, borinine, Ž . borine is studied using modern valence bond theory in its spin-coupled SC form. Three different types of SC wave functions-with six active orbitals and with four and eight active orbitals-are used to describe the system of the molecule and the -bond framework around the boron atom. It is demonstrated that the SC picture of the space in borabenzene is very similar to that in benzene: The spins of six distorted nonorthogonal 2 p orbitals are combined in a spin-coupling pattern involving two dominating Kekuletype and three less important Dewar-type Rumer spin functions. This indicates that it is appropriate to consider the -electron sextet in borabenzene as aromatic and that the reason for the reactivity of this molecule should lie with its framework. The two SC

Stereoselectivity in a series of 7‐alkylbicyclo[3.2.0]hept‐2‐enes: Experimental and computational perspectives

“…Monitoring changes in the spin-coupled wave functions for the si pathway as the reacting orbitals evolved over time, Karadakov and Cooper observed "the dominance of singlet diradical character over an extended range of geometries." [13] Carpenter [14] recently examined singlet diradicals that reside on a caldera, a broad shallow energy plateau. SCHEME 1 Thermal reactions of bicyclo[3.2.0]hept-2-ene (1) Although Carpenter proposes that these diradical species possess small amounts of excess energy, the "exact distribution" of this energy is highly influential on the product distributions.…”

“…Competitive isomerization and fragmentation processes at temperatures in excess of 300°C convert 1 to its isomer 2 or directly to fragments cyclopentadiene and ethylene (Scheme 1). [1,2] Determination of an accurate rate constant k 13 for the [1,3] rearrangement 1-to-2 and the associated Arrhenius parameters is complicated by the observation that 2 experiences facile Diels-Alder cycloreversion (retro Diels-Alder reaction) to cyclopentadiene and ethylene. Despite the large experimental error in activation energy for the [1,3] process, Cock and Frey conclude that the activation parameters for the sum (k 13 + k f ) are close to the expected values "if both processes have a biradical mechanism" and therefore that "a two-step pathway is competitive."…”

The Key Role of Orbital Interaction in Cooperativity between B⋅⋅⋅N and Hydrogen/Lithium Bonding: An ab initio Study

“…Borabenzene (C 5 H 5 B) is an interesting heteroaromatic compound which has been the subject of numerous experimental and theoretical studies . Although several adducts of C 5 H 5 B with donor molecules like N 2 and CO have been characterized,,, the base‐free borabenzene has never been reported, due to the electron deficiency and hence high Lewis acid properties of the boron atom.…”

“…Borabenzene (C 5 H 5 B) is an interesting heteroaromatic compound which has been the subject of numerous experimental and theoretical studies. [51][52][53][54] Although several adducts of C 5 H 5 B with donor molecules like N 2 and CO have been characterized, [52,55,56] the base-free borabenzene has never been reported, due to the electron deficiency and hence high Lewis acid properties of the boron atom. According to the quantum mechanical calculations, [55] the pronounced acceptor properties of C 5 H 5 B is mainly related to the presence of a vacant low-lying s* orbital on the boron atom.…”

Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)

“…Borabenzene (C 5 H 5 B) has been the subject of some experimental [1][2][3] and an even higher number of theoretical [4][5][6][7][8][9][10][11][12] studies; however, attempts to generate the free compound have met with failure so far. At least in two experimental studies, borabenzenze apparently occurred as a transient that was trapped either by dinitrogen [1] or pyridine.…”