Biology Forum Community General Discussion "H – C = C – H" doesn’t make sense chemically why?

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    • #9953
      MajesticQ
      Participant

      Help me understand why does the following structure fail to make sense chemically?

      H – C = C – H

      In my mind it would look something like this…

      (I’m self-studying from Campbell’s textbook, this is one of the questions at the end of the chapter. I read the chapter, can’t make sense of it all though)

      PS the right end of the image got cropped out here from some reason, but you can figure it out

    • #85486
      canalon
      Participant

      There is adiiference between H-C=C-H (impossible) and H-C=C-H (triple liaison in the last one, double in the first one). In fact look what you have drawn šŸ˜‰

    • #85496
      mith
      Participant

      carbon has 4 valence

    • #85564
      blcr11
      Participant

      As Mith points out, the full valence of carbon is 4. It will prefer to share its four electrons with its bonding partners. The structure as drawn has the carbons sharing only three electrons (one for each bond) which means that each carbon has a non-bonded electron. That makes it an acetylene diradical. Such a molecule may exist along some photochemical reaction path, and you can, Iā€™m sure, calculate its energy, which is undoubedly high relative to acetylene, but it is not a stable electonic structure for H2C2. The stable structure for H2C2 is acetylene or ethyne with a triple bond between the two carbons, as Canalon said.

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