[science123]

1) I thought it was Aromatic :- 6 pi electrons in a circle and all carbons have filled p orbitals. For some reason the answer is non-aromatic.

2) Again the answer was non-aromatic. Don't know why. It has 6 pi electrons and all carbons are sp2 in a circle. Do we count the electrons of C-O double bond?

3) No idea here. I don't know if we have to count the electrons of the side groups

4) If we count the lone pair then we would have 8 pi electrons making it anti-aromatic. Can the carbon with negative charge be sp3 instead to avoid anti-aromaticity and be non-aromatic thus more stable?

5) 2 pi electrons and all Carbons sp2 so i was thinking aromatic.

6) Again, I am not sure if we have to count the electrons of the carbonyl double bond.

7) same as 6

8.) Same problem as 4) Can the carbon be sp3 to avoid anti-aromaticity?

14) Not sure if that double bond can resonate and make 6 pi electrons

9) The resonance contributor is aromatic. Does that mean that the entire molecule is aromatic? What if the resonance contributor was anti-aromatic?

10) same as 9

11) Now the resonance contributor is anti aromatic so i guess i contributes to the hybrid less. What about the entire molecule? Is it anti aromatic too?

12) and 13) Not sure how to approach those. For 13, it has p orbitals filled and all carbons are sp2. but what e- to count?

[Jorriss]

A point on Huckel;s rule.

It predicts whether a planar molecule will be aromatic. Large ring structures that look as if they should be planar, may not be.

[kanonsviel]

I think the key word would be "Cyclic conjugation"
For 1) it's conjugated but not "cyclic" conjugated, so it's antiaromatic, and the conjugated pi electrons on the ring should be counted as 6.
For 2) it behaves like an aromatic system, but it seems like it's not considered to be an aromatic compound...the carbonyl carbon should be considered as an cation.

you may refer to the definition of "aromatic" in McMurry