C-C bond length in 1, 3-butadiene?

Question

Why is the bond length between the two central carbon atoms 146 pm instead of 154 pm?

Answer 1

Hi Haley. I hope you're doing well. 1,3-Butadiene is a conjugated molecule -- that is, it has alternating single and double bonds. In this case, the lewis structure is double, single, double. The Pi electrons in a conjugated molecule are shared by every carbon atom in the molecule, so, in reality, it is in/t alternating single and double bonds, but each bond is equivalent: more than a single bond, but less than a double bond...thus the bond is shorter than a normal single bond, because it has some double-bond character.

 

Hope that makes sense.

 

Best wishes

Raffi