Premium
The Quadruple Bonding in C 2 Reproduces the Properties of the Molecule
Author(s) -
Shaik Sason,
Danovich David,
Braida Benoit,
Hiberty Philippe C.
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.201600011
Subject(s) - quadruple bond , triple bond , single bond , bent bond , sextuple bond , three center two electron bond , bond energy , bond order , chemistry , bond dissociation energy , molecule , bond length , double bond , crystallography , bond strength , chemical bond , valence bond theory , bond , dissociation (chemistry) , molecular orbital , group (periodic table) , organic chemistry , adhesive , layer (electronics) , finance , economics
Ever since Lewis depicted the triple bond for acetylene, triple bonding has been considered as the highest limit of multiple bonding for main elements. Here we show that C 2 is bonded by a quadruple bond that can be distinctly characterized by valence‐bond (VB) calculations. We demonstrate that the quadruply‐bonded structure determines the key observables of the molecule, and accounts by itself for about 90 % of the molecule's bond dissociation energy, and for its bond lengths and its force constant. The quadruply‐bonded structure is made of two strong π bonds, one strong σ bond and a weaker fourth σ‐type bond, the bond strength of which is estimated as 17–21 kcal mol −1 . Alternative VB structures with double bonds; either two π bonds or one π bond and one σ bond lie at 129.5 and 106.1 kcal mol −1 , respectively, above the quadruply‐bonded structure, and they collapse to the latter structure given freedom to improve their double bonding by dative σ bonding. The usefulness of the quadruply‐bonded model is underscored by “predicting” the properties of the 3 Σ +ustate. C 2 ’s very high reactivity is rooted in its fourth weak bond. Thus, carbon and first‐row main elements are open to quadruple bonding!