"H - C = C - H" doesn't make sense chemically why? - Biology Forum

last updated by

blcr11 16 years, 4 months ago

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- August 12, 2008 at 4:14 pm #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
- August 12, 2008 at 7:55 pm #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 😉
- August 13, 2008 at 8:10 am #85496
  mith
  Participant
  carbon has 4 valence
- August 18, 2008 at 6:35 pm #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, I’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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