[MIA6]

1. Conjugated molecules -Butadiene, the central bond is shorter than a C-C single bond. C=C-C=C.
I don't understand why central bond is shorter? Because I think electrons are more spread out in central bond, whereas, in single bond, there are just two electrons and close to each other. But I still don't know why central bond here is not the single bond, i thought they refer to the same thing.
2."Each proton resonates with a different frequency." What does resonate mean? And is it related to resonance energy?

Thanks.

[savy2020]

Hello,
1.The structure of Butadiene is NOT C=C-C=C as written.
What I mean is that the pi electrons are not localized between the C1&C2 and C3&C4 i.e, If you observe the molecule then you would not see the pi electron density localised as above but indeed the pi electrons are delocalised and they are present also in the region between C2&C3 also. This can be understood in terms of electron cloud densities. The electron cloud is present in between all the carbon atoms. But using Lewis structures we cannot represent that delocalisation in a single structure since lewis diagrams talk of localised bonds and sharing of electrons. So we try to write the all possible structures changing the pi electrons here and there. These are called resonance contributors and the net molecule is called resonance hybrid.
The central bond is not single bond with only two electrons as depicted. But it is a bit more than single bond but less than double bond. i.e, it is a bond of characteristics in between single bond and double bond.
That's why its length is in between that of single and double bonds.
2. I'm sorry I've no idea about that{I'm in 12th grade and have not even a slight idea what means by "proton resonates"}

[MIA6]

thanks, but central bond should be shorter than the single bond. But you said "it is a bit more than single bond but less than double bond. i.e, it is a bond of characteristics in between single bond and double bond. That's why its length is in between that of single and double bonds." But It's not in between...

[savy2020]

b]it is a bit more than single bond but less than double bond.[/b]

What I mean is the characteristic of the bond  not bond length. As the bond order goes from 1 to 2 (single to double bond) the bond length decreases.

That's why its length is in between that of single and double bonds." But It's not in between...

In between doesn't mean exactly half way. What I mean is  1<bond order<2