C2 molecules have been found in vapour state. Their double bonds are made of two pi bonds because four electrons need to be accomodated in each bond. So this is against the rule that there must be a sigma bond before a pi bond is formed in the double bond. Why the anomoly?

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    $\begingroup$ Please reopen this question. This question wasn't about some high level research biradical stuff, but rather simple high school MOT theory application. $\endgroup$ Commented Apr 27, 2018 at 13:39
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    $\begingroup$ @GaurangTandon I am against reopening this question, especially for this reason; the C2 molecule has nothing to do with high school chemistry, it can only be understood with 'high level research biradical stuff' and there is still (and will probably forever be) a lot of debate about the bonding situation. Some say it's only a single bond, some say it's a double bond, there's arguments for the triple bond, and the believe for the quadruple bond. If you don't understand why this is the case, don't try apply 'simple high school MO theory'. $\endgroup$ Commented Apr 27, 2018 at 17:21
  • $\begingroup$ @Martin-マーチン I completely agree. The problem is that this is actually asked in Indian high school chemistry examinations(like JEE). Too bad we have to just remember these and move on without giving any thought to it. $\endgroup$
    – DatBoi
    Commented Apr 15, 2021 at 14:50


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