How many sigma and pi bonds are in xylene?

1 Answer
Truong-Son N.
Jun 21, 2016

There are 18 sigma and 3 pi bonds.

There are three isomers of xylene, but they all contain the same number of sigma and pi bonds.

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

An easy way to count these is to treat the skeletal structure as all sigma bonds, and add on pi bonds for each double bond in the major resonance structure.

So, taking m-xylene arbitrarily:

  • All hexagons have six sides, contributing 6 sigma bonds.
  • Each "C"-"H" bond on the benzene ring adds one sigma bond, for a total of 4.
  • The "C"-"C" bond with each methyl group counts as one sigma bond, contributing a total of 2 sigma bonds.
  • The three "C"-"H" bonds on each methyl group contribute a total of 6 more sigma bonds.

So, we have a total of 18 sigma bonds.

Inside the benzene ring, you have delocalized pi electrons over six atoms. The major resonance structure has three pi bonds; one for each double bond.

So the result is 18 sigma and 3 pi bonds.

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