Why is the structure provided aromatic?

Question

Provide a brief explanation of why the structure below is aromatic. Your answer should identify the hybridization of the oxygen atom and the carbon with the + charge, and account for which electrons are in the pi system.

Please explain in detail, thank you.

Answer 1

Hi Kat! To answer this question regarding the theory of aromaticity we'll have to take into account Huckel's rules.

1. A molecule must be flat
2. A molecule must be cyclic
3. A molecule must have a 2p orbital on each atom
4. A molecule must have (4 + 2n) pi electrons

Let's now go through these rules one at a time. The molecule we have is definitely flat and cyclic. Now let's see if there is a 2p orbital on every atom. The atoms that are engaged in sp2 hybridized double bonds have 2p orbitals (the alkene carbons). The oxygen in this case can either participate in sp3 or sp2 hybridization. If it has sp3 hybridization then it will be nonaromatic, but if it is sp2 hybridized then it will be aromatic or unusually stable. Lastly let's look at the carbocation. Since the carbon only has 3 bonds, it is in an sp2 trigonal planar formation so it also is participating in 2p orbitals.

Now let's look at rule 4. To count the number of pi electrons, we can first count the pi electrons that the alkene carbons are contributing. There are 4 carbons that are participating in alkene bonds, so there are 4 pi electrons from them. The oxygen is able to contribute 2 pi electrons because they are in the 2p orbital. Therefore this molecule has 6 pi electrons which follows the (4 + 2n) pi electrons rule.

Since all the requirements have been met, we can see that this molecule is aromatic.