The triply-bonded carbons in pyridyne and benzyne are sp-hybridised
the verdict
SUPPORTED
the evidence backs this
refutedsupported
the weight of evidence
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AS REPORTEDno primary record reached; this is what the reporting says
Reference material and expert chemical discussions confirm that the triply-bonded carbons in pyridyne and benzyne are sp-hybridised, despite being involved in highly strained ring systems with modified orbital overlap.
# Are the triply-bonded carbons in pyridyne (and benzyne) sp-hybridised?
Tags: organic-chemistry, hybridization
- Score: 9
- Views: 1436
- Answers: 2
- Answered: yes
- Asked by: Blue (301 rep)
- Asked: 2019-05-05
- Edited: 2019-05-06
- Site: chemistry
## Question
I was given this molecule (3,4-pyridyne) in a test:
I had to find out if it had any atoms which had a hybridization state other than sp2. The solution said that it doesn't have any. But aren't the triply-bonded carbon atoms sp-hybridized?
Edit:
Benzyne also has a similar structure, with a distorted triple bond -
## Answers
### Answer by orthocresol (score: 6 [ACCEPTED])
TL;DR It is sp-hybridised, but maybe not in the way we normally think of alkynes as being.
There are a couple of things to say before going into the actual answer.
Firstly, hybridisation is derived from geometry, not from the bonding pattern (in other words, how many σ- and π-bonds there are). In most cases, the bonding pattern dictates the geometry: for example, most saturated carbons are tetrahedral, and a tetrahedral geometry usually signals sp3 hybridisation, so saturated carbons are usually described as being sp3-hybridised. So, effectively,
Aryne
In organic chemistry, arynes and benzynes are a class of highly reactive chemical species derived from an aromatic ring by removal of two substituents. Arynes are examples of didehydroarenes (1,2-didehydroarenes in this case), although 1,3- and 1,4-didehydroarenes are also known. Arynes are examples of alkynes under high strain.
## Bonding in arynes
The alkyne representation of benzyne is the most widely encountered. Arynes are usually described as having a strained triple bond (left), but resonance contributors include a cumulene form (middle) and biradical form (right):
Geometric constraints on the triple bond in benzyne result in diminished overlap of in-plane p-orbitals, and thus weaker triple bond. The vibrational frequency of the triple bond in benzyne was assigned by Radziszewski to be 1846 cm−1, indicating a weaker triple bond than in unstrained alkyne with vibrational frequency of approximately 2150 cm−1. Nevertheless, benzyne is more like a strained alkyne than a diradical, as seen from the large singlet–triplet gap and alkyne-like reactivity.
The LUMO of aryne lies much lower than the LUMO of unstrained alkynes, which makes it a better energy match for the HOM
Everything we examined (2)
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