The ‘Inverted Bond’ revisited. Analysis of ‘in silico’ models and of [1.1.1]Propellane using Orbital Forces

10.26434/chemrxiv.7215269.v4 ◽

2019 ◽

Author(s):

Rubén Laplaza ◽

Julia Contreras-García ◽

Franck Fuster ◽

François Volatron ◽

Patrick Chaquin

Keyword(s):

Total Energy ◽

Molecular Orbital ◽

In Silico ◽

Bond Energies ◽

Parent Molecule ◽

Ca 50 ◽

In Silico Models ◽

Mo Theory

<div>This article dwells on the nature of “inverted bonds”, which make reference to the σ interaction between two s-p hybrids by their smaller lobes, and their presence in [1.1.1]propellane 1. Firstly we study H 3 C-C models of C-C bonds with frozen HCC angles reproducing the constraints of various degrees of “inversion”. Secondly, the molecular orbital (MO) properties of [1.1.1]propellane 1 and [1.1.1]bicyclopentane 2 are analyzed with the help of orbital forces as a criterion of bonding/antibonding character and as a basis to evaluate bond energies. Triplet and cationic state of 1 species are also considered to confirm the bonding/antibonding character of MOs in the parent molecule. These approaches show an essentially non-bonding character of the σ central CC interaction in propellane. Within MO theory, this bonding is thus only due to π-type MOs (also called ‘banana’ MOs or ‘bridge’ MOs) and its total energy is evaluated to ca. 50 kcal/mol. In bicyclopentane 2, despite a strong σ-type repulsion, a weak bonding (15-20 kcal/mol) exists between both central CC, also due to π-type interactions, though no bond is present in the Lewis structure. Overall, the so-called ‘inverted’ bond, as resulting from a σ overlap of the two s-p hybrids by their smaller lobes, appears highly questionable.</div>

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The ‘Inverted Bond’ revisited. Analysis of ‘in silico’ models and of [1.1.1]Propellane using Orbital Forces

10.26434/chemrxiv.7215269.v3 ◽

2019 ◽

Author(s):

Rubén Laplaza ◽

Julia Contreras-García ◽

Franck Fuster ◽

François Volatron ◽

Patrick Chaquin

Keyword(s):

Total Energy ◽

Molecular Orbital ◽

In Silico ◽

Bond Energies ◽

Parent Molecule ◽

Ca 50 ◽

In Silico Models ◽

Mo Theory

<div>This article dwells on the nature of “inverted bonds”, which make reference to the σ interaction between two s-p hybrids by their smaller lobes, and their presence in [1.1.1]propellane 1. Firstly we study H 3 C-C models of C-C bonds with frozen HCC angles reproducing the constraints of various degrees of “inversion”. Secondly, the molecular orbital (MO) properties of [1.1.1]propellane 1 and [1.1.1]bicyclopentane 2 are analyzed with the help of orbital forces as a criterion of bonding/antibonding character and as a basis to evaluate bond energies. Triplet and cationic state of 1 species are also considered to confirm the bonding/antibonding character of MOs in the parent molecule. These approaches show an essentially non-bonding character of the σ central CC interaction in propellane. Within MO theory, this bonding is thus only due to π-type MOs (also called ‘banana’ MOs or ‘bridge’ MOs) and its total energy is evaluated to ca. 50 kcal/mol. In bicyclopentane 2, despite a strong σ-type repulsion, a weak bonding (15-20 kcal/mol) exists between both central CC, also due to π-type interactions, though no bond is present in the Lewis structure. Overall, the so-called ‘inverted’ bond, as resulting from a σ overlap of the two s-p hybrids by their smaller lobes, appears highly questionable.</div>

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The ‘Inverted Bond’ revisited. Analysis of ‘in silico’ models and of [1.1.1]Propellane using Orbital Forces

10.26434/chemrxiv.7215269.v2 ◽

2019 ◽

Author(s):

Rubén Laplaza ◽

Julia Contreras-García ◽

Franck Fuster ◽

François Volatron ◽

Patrick Chaquin

Keyword(s):

Total Energy ◽

Molecular Orbital ◽

In Silico ◽

Bond Energies ◽

Parent Molecule ◽

Ca 50 ◽

In Silico Models ◽

Mo Theory

<div>This article dwells on the nature of “inverted bonds”, which make reference to the σ interaction between two s-p hybrids by their smaller lobes, and their presence in [1.1.1]propellane 1. Firstly we study H 3 C-C models of C-C bonds with frozen HCC angles reproducing the constraints of various degrees of “inversion”. Secondly, the molecular orbital (MO) properties of [1.1.1]propellane 1 and [1.1.1]bicyclopentane 2 are analyzed with the help of orbital forces as a criterion of bonding/antibonding character and as a basis to evaluate bond energies. Triplet and cationic state of 1 species are also considered to confirm the bonding/antibonding character of MOs in the parent molecule. These approaches show an essentially non-bonding character of the σ central CC interaction in propellane. Within MO theory, this bonding is thus only due to π-type MOs (also called ‘banana’ MOs or ‘bridge’ MOs) and its total energy is evaluated to ca. 50 kcal/mol. In bicyclopentane 2, despite a strong σ-type repulsion, a weak bonding (15-20 kcal/mol) exists between both central CC, also due to π-type interactions, though no bond is present in the Lewis structure. Overall, the so-called ‘inverted’ bond, as resulting from a σ overlap of the two s-p hybrids by their smaller lobes, appears highly questionable.</div>

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The molecular orbital theory of chemical valency XX. The energy in higher approximations

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1955.0144 ◽

1955 ◽

Vol 230 (1182) ◽

pp. 424-428 ◽

Cited By ~ 3

Keyword(s):

Wave Function ◽

Total Energy ◽

Molecular Orbital ◽

Molecular Orbital Theory ◽

Bond Energies ◽

Orbital Theory ◽

Conjugated Molecules ◽

Approximate Wave Function ◽

Approximate Wave

The equations determining the optimum orbitals in a many-determinant approximate wave function are given and their relation to the total energy considered. As expected, the form of the energy shows that bond energies will be nearly additive in non-conjugated molecules as long as they are not strongly polar, but that this will not be so for conjugated molecules.

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Bonding Analysis in [1.1.1]Propellane and [1.1.1]Bicyclopentane Using Orbital Forces. The Myth of the “Inverted Bond”

10.26434/chemrxiv.7215269.v1 ◽

2018 ◽

Author(s):

Rubén Laplaza ◽

Julia Contreras-García ◽

Franck Fuster ◽

François Volatron ◽

Patrick Chaquin

Keyword(s):

Triplet State ◽

Total Energy ◽

Molecular Orbital ◽

Physical Basis ◽

Bond Energies ◽

Bonding Analysis

The properties of the “inverted bond” in [1.1.1]propellane are investigated by two methods. Firstly we study H3C-C models of C-C bonds with frozen HCC angles reproducing the constraints of various degrees of “inversion”. Secondly, the molecular orbital (MO) properties of [1.1.1]propellane and [1.1.1]bicyclopentane are analyzed with the help of orbital forces as a criterion of bonding/antibonding character and as a basis to evaluate in-situ bond energies. Triplet state of propellane and cationic states of propellane and bicyclopentane are also considered to comfort the bonding/antibonding character of MOs in the parent molecules. Both approaches shows an essentially nonbonding or slightly repulsive character of the sigma central CC interaction in propellane: the so-called ‘inverted’ bond, as resulting from a sigma overlap of the two s-p hybrids by their smaller lobes, appears devoid of physical basis. The bonding of central CC in propellane is thus only due to pi-type MOs (also called ‘banana’ MOs or ‘bridge’ MOs) and its total energy is evaluated to ca. 60 kcal/mol. In bicyclopentane, despite a strong sigma-type repulsion, a weak bonding (20 kcal/mol) exists between both central CC, also due to pi-type interactions, though no formal bond is present

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Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

10.26434/chemrxiv.11446224 ◽

2019 ◽

Author(s):

Ishita Bhattacharjee ◽

Debashree Ghosh ◽

Ankan Paul

Keyword(s):

Excited State ◽

Potential Energy ◽

Molecular Orbital ◽

High Spin ◽

Potential Energy Surfaces ◽

Valence Bond ◽

Deep Minimum ◽

State Potential ◽

Energy Surfaces ◽

Mo Theory

The question of quadruple bonding in C2 has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C2, N2 and Be2 and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the 2S+1Σg/u (with 2S+1=1,3,5,7,9) states of C2 and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N2 and HC≡CH, the presence of a deep minimum in the 7Σ state of C2 and CN+ suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

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