How do you count sigma and pi bonds? For example, in the lewis structure azidothymidine there are 33 sigma and 5 pi bonds. How is this found?

1 Answer
Truong-Son N.
Feb 9, 2016

Azidothymidine:

![https://upload.wikimedia.org/](useruploads.socratic.org)

When you draw the purely skeletal structure, i.e. with no double or triple bonds, what is there counts as one sigma bond per single bond.

That gives you:

  • Five "C"-"O" sigma bonds
  • Six "C"-"N" sigma bonds
  • Two "N"-"N" sigma bonds
  • One "N"-"H" sigma bond
  • One "O"-"H" sigma bond
  • Seven "C"-"C" sigma bonds

And don't forget the implicit hydrogens!

  • Eleven "C"-"H" sigma bonds

Now when you consider pi bonds, it is one additional pi bond for each additional bond for up to only double and triple bonds:

  • Two "N"-"N" pi bonds
  • One "C"-"C" pi bond
  • Two "C"="O" pi bonds

So we have:

  • 5 + 6 + 2 + 1 + 1 + 7 + 11 = 33 sigma bonds
  • 2 + 1 + 2 = 5 pi bonds
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