hi why is that cyclobutadiene doesn't have resonance forms? If possible, explain it using the Valence Bond Theory as opposed to the Molecular orbital theory

To explain why cyclobutadiene is not aromatic requires one to talk about molecular orbitals, unfortunately, since resonance, conjugation and aromaticity are based on molecular orbital theory.

 

Basically, the four p-orbitals on each of the four carbon atoms will form four Pi orbitals, a bonding orbital, two non-bonding orbitals, and an antibonding orbital. Since each p-orbital contributes one electron to the Pi system, there will be four electrons: the first two fill the bonding orbital, so the other two go into the non-bonding orbital. However, since the two non-bonding electrons will go into opposite orbitals, this makes cyclobutadiene a highly-unstable diradical species (hence, cyclobutadiene is known as an anti-aromatic molecule, a molecule which becomes highly unstable when it forms a cyclic conjugated Pi system).

 

Since the formation of this conjugated Pi system is so unfavorable, cyclobutadiene will adopt a conformation which prevents the two adjacenct pi bonds from becomming conjugated. Since conjugation is essentially resonance, cyclobutadiene will not have a resonance form.

a simple rule is that for resonance to be achieved, 4n+2 (where n=any integer) electrons must be in a conjugated pi system

i thought that was required to be aromatic..?

wow, i am so sorry. that was a pretty bad slip. i meant aromaticity

Along the same lines, molecules with 4n electrons in a cyclic conjugated pi system are anti-aromatic.

ok, another unrelated question but didn't want to start up another thread in fear of spam.

 

It's about hybridisation:

 

Take for example CH3+, carbon here would be sp2 hybridized correct? Since it appears that it would sit in a planar, and thus has an empty p orbital. OH-'s Oxygen would be sp3 hybridized since it would have 3 lone pairs and one sigma bond, and it would resemble a tetrahedral shape.

 

So when CH3(+) + OH(-) -> CH4O, you end up with carbon's empty p orbital overlapping Oxygen's sp3 orbital and a sigma bond is formed. How does this work? The net result is that both Carbon and Oxygen becomes sp3 hybridized.