I was reading this page at Chemwiki; there they were discussing conjugated-$\pi$ bond.
In order to show that conjugation requires alternate double bonding, they cited the example of 1,3,6-heptatriene:
To be considered conjugated, two or more π bonds must be separated by only one single bond – in other words, there cannot be an intervening sp$^3$-hybridized carbon, because this would break up the overlapping system of parallel 2p$_z$ orbitals. In the compound below, for example, the C1-C2 and C3-C4 double bonds are conjugated, while the C6-C7 double bond is considered to be isolated, due to the effect of the sp$^3$-hybridized C5.
I've a problem with their explanation; firstly are they following MO theory or VB theory? While describing molecules with MO, they, suddenly from nowhere, used the concept of hybridisation. Why?
Can anyone explain only with he help of MO theory why, there needs to be alternate $\pi$ bonding in the molecule for conjugation to happen without use of hybeidisation?