Molecules that are arranged in the shape of a ring can be described as one of three things: completely aromatic, anti-aromatic, and non-aromatic. Their descriptions are as follows.
Aromaticity has four major criteria. In order for a molecule to be considered aromatic, it must:
1. Be cyclic
- This means the molecule’s carbon atoms are arranged in the shape of a hexagon1.
2. Be planar
- In short, this means that the molecule must be flat. In order for it to be flat, all atoms in the ring must have a p orbital, and all p orbitals must be aligned. A p orbital is kind of like a tiny atmosphere floating above the atom, which houses a π electron (a negatively charged particle). Because the electrons are negative, you might think of them as angry little birds. Just as you wouldn’t want too many angry little birds in the same cramped area of sky, you don’t want lots of negative charge from electrons too close together…neither make for a desirable environment! Therefore, it would be better to spread out the little birds (or electrons). When the p orbitals are aligned, the density of the negative charges can be spread out, or delocalized2; this makes the molecules more stable…this is a very good thing!
3. Be completely conjugated
- For a molecule to be conjugated, every atom must have a p orbital2…its own tiny atmosphere.
4. Satisfy Huckel’s rule
- Huckel’s rule says the compound must contain 4n + 2 electrons in order to be aromatic2. That means that as long as the molecule contains a number of electrons (those found in the p orbital) that is a multiple of 4n + 2, it meets the fourth criteria for aromaticity.
If a compound meets the first three criteria, but contains 4n π electrons (or birds) rather than 4n + 2, it is said to be an antiaromatic compound.3 Should a compound fail to meet one or more of the requirements it is nonaromatic.3
1Smith, J. Organic Chemistry. 2nd ed.; McGraw-Hill, 2008, pp 616.
2Smith, J. Organic Chemistry. 2nd ed.; McGraw-Hill, 2008, pp 617.
3Smith, J. Organic Chemistry. 2nd ed.; McGraw-Hill, 2008, pp 618.
I think you did a pretty good job at describing aromaticity. If I wasn't very familiar with Chemistry I think I would get a good grasp on the meaning of aromaticity and what it takes to make the compound aromatic. I love how you listed your sources at the end and showed where they were used in your explanation. This is very helpful. It allows the reader to do additional reading if they need more of an explanation to help them understand. I think it would have been a bit more helpful if you went into more detail on cyclic, conjugated, and Huckel's rule, the reader would be able to understand the concept to a greater extent. I think those three things may remain a little muddy to someone that has no chemical background. Overall you did a good job! I think you would make a good teacher. :-)
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