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Quadruple bond between two carbon atoms

by piercebeatz
Tags: atoms, bond, carbon, dicarbon, quadruple
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piercebeatz
#1
Nov23-13, 03:47 PM
P: 232
I was wondering if a quadruple bond between two carbon atoms would be possible. I found this on wikipedia about "dicarbon": http://en.wikipedia.org/wiki/Diatomic_carbon, which is related to this question, since what I'm describing is an isomer of dicarbon. Anyone have any ideas?
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DrDu
#2
Nov24-13, 03:16 AM
Sci Advisor
P: 3,560
The wikipedia article is not very good. Valence bond theory also predicts a double bond as carbon atoms have two unpaired electrons. It is not a requirement of VB theory for the molecule to obey the octet rule.
Higher bond orders may be present in electronically excited state of C2.
piercebeatz
#3
Nov24-13, 09:34 AM
P: 232
So what do you think about a quadruple bond?

hilbert2
#4
Nov24-13, 10:50 AM
P: 326
Quadruple bond between two carbon atoms

Whether bonding in dicarbon is better described as a double or quadruple bond is still being debated, see http://www.ch.imperial.ac.uk/rzepa/blog/?p=10733 .

Assigning definite integer-valued bond orders to chemical bonds is just a property of the approximative model used to describe bonding.
cgk
#5
Nov25-13, 02:29 AM
P: 419
Whatever else one may or may not say about C2, if it is described with a single closed-shell determinant wave function (i.e., with Hartree-Fock or Kohn-Sham), one can rotate its occupied orbitals into two equivalent doubly-occupied non-standard sigma bond orbitals and two standard doubly occupied pi bond orbitals via orbital localization (Pipek-Mezey-like).

As the theoretical basis for bond order concept is closely related to this form of MO theory (which, for C2, is not entirely beyond question--it has low lying excited states), one could formally interpret this as a quadruple bond. Or as a double bond or triple bond, depending on how one wishes to interpret the non-standard sigma system.

In short, it is the perfect fighting ground for bored theorists 8).
DrDu
#6
Nov25-13, 05:42 AM
Sci Advisor
P: 3,560
Another question is what a number like "bond order" really tells you.
What we observe are bond lengths and strengths and not bond orders.


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