What forces cyclooctatetraene into it’s tub-shaped structure? I understand the consequences of the tub shape in relation to it’s ability for p orbital overlap, but I don’t understand what forces it to be tub-shaped? (Mostly avoiding anti-aromaticity. - GS).

Do you have any tips on how to distinguish aromatic, antiaromatic, and nonaromatic?  (Use Huckel rule. - GS).

What is the significance of a sigma complex? (It is formed at the rate-limiting step of aromatic electrophilic substitution and where the electrophile is bonded by a sigma-bond. . - GS).

Dr. Sereda, I am still a bit confused on the counting of electrons on aromatic and antiaromic species. When a triangle, square, or hexagon has a + sign somewhere on the molecule, does that not contribute to counting of electrons? (It does contribute, because electrons carry a negative charge. - GS). Furthermore, does a - symbol count as two electrons? (No. It means that the structure has one more electron, than its neutral analogue. For instance, cyclopentadienyl-cation with 4 electrons has one less electron, than its neutral analogue - free radical with 5 electrons. Cyclopentadienyl-anion with 6 electrons has one more electron, than its neutral analogue - free radical with 5 electrons. - GS).

Is it true that for Huckel’s rule, if you solve for n and obtain a fraction, that it does not work? (No. The rule still works. It means that the system is not aromatic or it is antiaromatic. If you want to challenge the rule, make the system non-planar, or break the continuous conjugation by sp3 atoms, or introduce a bunch of additional cycles (polycyclic system). - GS).

Dr. Sereda, I am mostly understanding Huckel’s rule, however, I am unsure of what integer to plug in. I understand that it can be 0, 1, 2, 3, etc.. but how do you know when to plug in 0 for n, versus when to plug in 1 or 2? (If N is number of electrons, the integer n can be found from the equation: N=4n+2 or n=(N-2)/4  - GS).

Dr. Sereda, what causes a compound to absorb UV-light at the highest and longest intensity? (Generally speaking, the “transition moment”, which is related to the overlap of wavefunctions of the ground and excited states, determines intensity of absorption. For linear conjugated polyenes - it is simply the number of C=C bonds in continuous conjugation. - GS).