Talk:Diatomic carbon

Confusing!!

Quote:"...molecular orbital theory shows that there are two sets of paired electrons in the sigma system (one bonding, one antibonding), and two sets of paired electrons in a degenerate pi bonding set of orbitals. This adds up to give a bond order of 2, meaning that there exists a double bond between the two carbons in a C2 molecule." "This is surprising because the MO diagram of diatomic carbon would show that there are two pi bonds and no sigma bonds." How can Molecular Orbital theory predict that the two pi orbitals are bonding (net order 2) and the sigma bonding and antibonding have no net contribution BUT the MO diagram does not show it? !!! I believe that this can NOT be correct. You just put in the sigma levels, bonding and anti and also put in the pi bonding orbitals. The statement as written can not be correct. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~π __ __ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . π ↑↓ ↑↓ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~σ ↑↓ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . σ ↑↓ MO Theory and Diagram must agree if done correctly, right?216.96.76.60 (talk) 19:58, 17 February 2013 (UTC)

Properties

Can it exist at room temperature? What is boiling nd melting point? — Preceding unsigned comment added by 79.191.191.243 (talk) 23:20, 23 October 2013 (UTC)

Sure it exists at room temperature. If you read the article, you'll see that due to its autoplymersation, you can't accumulate the bulk substance, and thus cannot find the boiling and melting points experimentally. Plasmic Physics (talk) 23:52, 23 October 2013 (UTC)

"It is a gas that only exists above 3,642 °C"

I didn't know "blue hydrocarbon flames" are that hot. — Preceding unsigned comment added by Stankot (talk • contribs) 20:43, 12 March 2016 (UTC)

3.642 kilocelsius Example99 (talk) 08:25, 5 February 2023 (UTC)

Formulaic concern

In the second row of the article, dicarbon is drawn with a triple bond between the carbon atoms, contrary to double bond of the drawing in the box just on the right, and to what is stated in the text of the article. In addition, as for the molecular orbital description of the same bond, it seems to me incomplete and not clear; perhaps a M.O. diagram could be profitable. Ekisbares (talk) 10:45, 24 November 2014 (UTC)

Although the triplet ground-state is bound by a double bond, the singlet excited-state is apparently very close in energy. The singlet state is chosen to be represented by the formula as it represents the most completely electronically paired state for simplicity. Plasmic Physics (talk) 04:14, 25 November 2014 (UTC)

Thanks for this answer, Plasmic Physics. The reason I came onto the talk page was because I had the same question as Ekisbares. I think something along the lines of your answer given here would be fitting on the main article if placed as a side note or in parentheses, as I can see it being assumed to be a mistake. I'm unsure how to reword to be a bit simpler or perhaps slightly shorter, otherwise I'd have done it myself That kiwi guy (talk) 08:31, 17 January 2015 (UTC)

OK, but I've since changed my mind. In hind sight, it seems like a rather silly reason. Plasmic Physics (talk) 20:22, 17 January 2015 (UTC)

Why would C
₂ be bonded doubly?

With the nonbonding electron pair, neither carbon reaches the octet. 80.98.179.160 (talk) 09:47, 26 March 2018 (UTC)

There are several cited refs in the § Chemistry section that discuss it from various computational analyses. Some of them presumably discuss the "why" (what specific energy detail is less stable in other bonding patterns). DMacks (talk) 14:49, 26 March 2018 (UTC)

The references are somewhat out of date - for example, quadruple bond has been asserted by Shaik et al 2016 (https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.201600011) and Miyamoto et al 2020 (https://www.nature.com/articles/s41467-020-16025-x). Is this still a contentious issue?NiKChE (talk) 12:20, 9 February 2021 (UTC)

is c2 smiles c$c i think so what about u

in 5/2/23 (dmy) we will decide if we will change the smiles Example99 (talk) 15:52, 28 January 2023 (UTC)

Based on cited refs, a quadruple-bond is possible but disputed. Double is better-supported by multiple refs and lines of reasoning. DMacks (talk) 17:13, 28 January 2023 (UTC)

thx for that man Example99 (talk) 17:59, 28 January 2023 (UTC)

You're welcome! Always happy to chat chemistry. DMacks (talk) 18:29, 28 January 2023 (UTC)

i know its a 4x bond u dummy Example99 (talk) 12:23, 30 January 2023 (UTC)

i said it 2x and u only 1x so i win Example99 (talk) 08:36, 5 February 2023 (UTC)

Spectral Lines

Where are the sources coming from for the transitions in the EM properties table? Some I know to be real, i.e. d3Πg→a3Πu at 518.0 nm is the Swan band (albeit usually quoted with the v00 wavelength of 516.0 nm) and C1Πg→A1Πu at 386.6 nm is the Deslandres-d'Azambuja band. However, I cannot find a single source for the alleged C1Πg→a3Πu transition, the C1Πg→c3Σ+u transition, the d3Πg→A1Πu transition, and possibly others in the table that I haven't examined. My concern is that emission wavelengths were calculated simply off of the differences in the state energy levels with no consideration to transition rules/forbidden transitions, and that those transitions do not occur. If indeed there is a source, then it needs to be added to the references for the article and clearly linked to the table/specific transitions that it covers. And, it should be subject to greater scrutiny, since those particular transitions are not present in other literature. I suggest the following options as references for known C2 transitions.

The Spectroscopy of C2: A Cosmic Beacon Timothy W. Schmidt Accounts of Chemical Research 2021 54 (3), 481-489 DOI: 10.1021/acs.accounts.0c00703

Huber, K.., Herzberg, Gerhard., Huber, Klaus-Peter. Molecular Spectra and Molecular Structure: IV. Constants of Diatomic Molecules. United Kingdom: Springer US, 1979. Spectralquandry (talk) 19:22, 11 April 2023 (UTC)

Perhaps @Plasmic Physics: who put this table in, can say what the source of information is. Graeme Bartlett (talk) 21:53, 11 April 2023 (UTC)

Their last edit was in January 2021. DMacks (talk) 22:46, 11 April 2023 (UTC)