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The Chemical Bond in C 2
Author(s) -
Hermann Markus,
Frenking Gernot
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201503762
Subject(s) - three center two electron bond , triple bond , chemistry , chemical bond , single bond , bond order , valence bond theory , sextuple bond , acetylene , generalized valence bond , bond dissociation energy , quadruple bond , computational chemistry , bond , dissociation (chemistry) , bond energy , crystallography , bond length , molecule , double bond , molecular orbital , group (periodic table) , crystal structure , organic chemistry , finance , economics
Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for H n CCH n ( n =0–3) and N 2 . The quadratic force constants and the stretching potentials of H n CCH n have been calculated at the CASSCF/cc‐pVTZ level. The bond dissociation energies of the C−C bonds of C 2 and HC≡CH were computed using explicitly correlated CASPT2‐F12/cc‐pVTZ‐F12 wave functions. The bond dissociation energies and the force constants suggest that C 2 has a weaker C−C bond than acetylene. The analysis of the CASSCF wavefunctions in conjunction with the effective bond orders of the multiple bonds shows that there are four bonding components in C 2 , while there are only three in acetylene and in N 2 . The bonding components in C 2 consist of two weakly bonding σ bonds and two electron‐sharing π bonds. The bonding situation in C 2 can be described with the σ bonds in Be 2 that are enforced by two π bonds. There is no single Lewis structure that adequately depicts the bonding situation in C 2 . The assignment of quadruple bonding in C 2 is misleading, because the bond is weaker than the triple bond in HC≡CH.