Question

Which of the following will need to be counted when determining the total number of pi electrons in a conjugated system? (choose all that apply)--assume that the pi system is a series of atoms with p orbitals available.

Answer 1

1,3-butadiene is the simplest example of a system of conjugated pi bonds. To be considered conjugated, two or more pi bonds must be separated by only one single bond – in other words, there cannot be an intervening sp3-hybridized carbon, because this would break up the overlapping system of parallel p orbitals.

A very important concept to keep in mind is that there is an inherent thermodynamic stability associated with conjugation. This stability can be measured experimentally by comparing the  heat of hydrogenation of two different dienes.

Number of double bonds and lone pair of electrons need  to be counted when determining the total number of pi electrons in a conjugated system.