The Nature of the Fourth Bond in the Ground State of C<sub>2</sub>: The Quadruple Bond Conundrum

Danovich, David; Hiberty, Philippe C.; Wu, Wei; Rzepa, Henry; Shaik, Sason

doi:10.1002/chem.201400356

Cited by 88 publications

(149 citation statements)

References 79 publications

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“…Since w PP is calculated in the Kotani spin basis, which is orthonormal, the PP weight is well defined and does not suffer from the ambiguities associated with the use of Rumer spin functions. 3 The same trend is found for the "Atomic" orbital ordering and associated spin function (αβαβαααβββ): w PP = 0.794 (full valence) versus 0.874 (triple bond), with the decrease being slightly larger for this restricted orbital/spin coupling wave function than for the "Paired" orbital/PP spin coupling wave function.…”

Section: Full Valence (Ten Electrons Ten Orbitals) Gvbsupporting

confidence: 64%

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

Dunning

2016

J. Phys. Chem. A

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The inertness of molecular nitrogen and the reactivity of acetylene suggest there are significant variations in the nature of triple bonds. To understand these differences, we performed generalized valence bond as well as more accurate electronic structure calculations on three molecules with putative triple bonds: N2, HCN, and HC2H. The calculations predict that the triple bond in HC2H is quite different from the triple bond in N2, with HCN being an intermediate case but closer to N2 than HC2H. The triple bond in N2 is a traditional triple bond with the spins of the electrons in the bonding orbital pairs predominantly singlet coupled in the GVB wave function (92%). In HC2H, however, there is a substantial amount of residual CH(a(4)Σ(-)) fragment coupling in the triple bond at its equilibrium geometry with the contribution of the perfect pairing spin function dropping to 82% (77% in a full valence GVB calculation). This difference in the nature of the triple bond in N2 and HC2H may well be responsible for the differences in the reactivities of N2 and HC2H.

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Section: Full Valence (Ten Electrons Ten Orbitals) Gvbsupporting

confidence: 64%

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

Dunning

2016

J. Phys. Chem. A

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“…[16] However, it is important to note that scientific arguments, debates, and controversies are at the heart of chemistry. This situation has been clearly stated in the very recent paper entitled "The Nature of the Fourth Bond in the Ground State of C 2 : The Quadruple Bond Conundrum" by Danovich et al, [17] in which these authors recongnize that they are in front of a "Rashomon effect", in which the bonding picture is becoming too fuzzy to be constructive anymore.…”

Section: Introductionmentioning

confidence: 97%

A Complete NCI Perspective: From New Bonds to Reactivity

Narth¹,

Maroun²,

Boto³

et al. 2016

Challenges and Advances in Computational Chemistry and Physics

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The Non-Covalent Interaction (NCI) index is a new topological tool that has recently been added to the theoretical chemist's arsenal. NCI fills a gap that existed within topological methods for the visualization of non-covalent interactions. Based on the electron density and its derivatives, it is able to reveal both attractive and repulsive interactions in the shape of isosurfaces, whose color code reveals the nature of the interaction. It is interesting to note that NCI can even be calculated at the promolecular level, making it a suitable tool for big systems, such as proteins or DNA. Within this chapter we will review the main characteristics of NCI, its similarities with and differences from previous approaches. Special attention will be paid to the visualization of new interaction types. Being based on the electron density, NCI is not only very stable with respect to the calculation method, but it is also a suitable tool for detecting new bonding mechanisms, since all such mechanisms should have a detectable effect on the electron density. This type of approach overcomes the limitations of bond definition, revealing all interaction types, irrespective of whether they have a name or have previously been identified. Finally, we will show how this tool can be used to understand chemical change along a chemical reaction. We will show several examples of torquoselectivity and put forward an explanation of selectivity based on secondary interactions which is complementary to the historical orbital approach.A complete NCI perspective: from new bonds to reactivity 3

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“…[1][2][3][4][5][6][7][8][9][10][11] According to Shaik et al, [1][2][3][4] in its X 1 † C g ground state C 2 features a quadruple bond comprised of two bonds and two bonds. However, despite its higher multiplicity, this quadruple bond is weaker than the triple carbon-carbon bond in ground-state ethyne, C 2 H 2 , which has a higher force constant and a shorter bond length.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Shielding Studies of C₂ and C₂H₂ Support Higher than Triple Bond Multiplicity in C₂

Karadakov

Kirsopp

2017

Chemistry A European J

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The carbon-carbon bonds in the ground states of C 2 and C 2 H 2 , at their equilibrium geometries, are compared by analysing the changes in the off-nucleus magnetic shielding tensor within the space surrounding each of these molecules. A wide range of quantum-chemical approaches, including full-valence CASSCF-GIAO, CCSD(T)-GIAO and CCSDT-GIAO, all with the cc-pVQZ basis set, as well as HF-GIAO and MP2-GIAO, with the cc-pVQZ, cc-pV5Z and cc-pV6Z basis sets, show that the surroundings of the carbon-carbon bond in C 2 are more shielded than those of the carbon-carbon bond in C 2 H 2 . The additional shielding of the carbon-carbon bond in C 2 is found to be due to a larger paramagnetic contribution to component of the shielding tensor which is perpendicular to the molecular axis. The analysis of the off-nucleus shielding data indicates that the carbon-carbon bond in C 2 is "bulkier" and, therefore, of a higher multiplicity, but weaker than the corresponding bond in C 2 H 2 . According to the results of the shielding calculations, the carbon nuclei in C 2 should be much more shielded than those in C 2 H 2 , with 13 C isotropic magnetic shieldings in the ca. 224-227 ppm and ca. 123-125 ppm ranges for C 2 and C 2 H 2 , respectively.

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The Nature of the Fourth Bond in the Ground State of C₂: The Quadruple Bond Conundrum

Cited by 88 publications

References 79 publications

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

A Complete NCI Perspective: From New Bonds to Reactivity

Magnetic Shielding Studies of C₂ and C₂H₂ Support Higher than Triple Bond Multiplicity in C₂

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The Nature of the Fourth Bond in the Ground State of C2: The Quadruple Bond Conundrum

Cited by 88 publications

References 79 publications

Variations in the Nature of Triple Bonds: The N2, HCN, and HC2H Series

Variations in the Nature of Triple Bonds: The N2, HCN, and HC2H Series

A Complete NCI Perspective: From New Bonds to Reactivity

Magnetic Shielding Studies of C2 and C2H2 Support Higher than Triple Bond Multiplicity in C2

Contact Info

Product

Resources

About

The Nature of the Fourth Bond in the Ground State of C₂: The Quadruple Bond Conundrum

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

Variations in the Nature of Triple Bonds: The N₂, HCN, and HC₂H Series

Magnetic Shielding Studies of C₂ and C₂H₂ Support Higher than Triple Bond Multiplicity in C₂