Provide a brief explanation of why the dianion (below) is antiaromatic.

Question

Provide a brief explanation of why the dianion (below) is antiaromatic. Your answer should identify the hybridization of each carbon atom and account for which electrons are in the pi system.

Answer 1

I think this question is incorrect. Please double check it. Note there is a huge difference between "antiaromatic" and "nonaromatic." Antiaromatic compounds are inherently unstable, and aside from structures that cannot escape planarity (such as cyclobutadiene) are not realistic. Cyclooctatetrane could be antiaromatic, but since it has flexibility, is not actually planar and therefore is nonaromatic. Every textbook I've ever used had this example drawn out.

Plus, your example has 10 pi electrons, so could actually be aromatic if planar.

Answer 2

Antiaromatic compounds have 4n π electrons whereas

Aromatic compounds have [4n + 2] π electrons. Aromatic compounds have pi electrons of numbers 2, 6, 10, 14, 18, 22, 26, etc.

Let's count the pi electrons in this compound. Each double bond can be counted for 2 pi electrons, so that gives us 6. The negative charge is another 2 pi electrons for a total of 8. 8 is a multiple of 4n (4*2) and not [4n+2], making it antiaromatic.

For hybridization, C=C double bonds are examples of sp² hybridization. This gives a trigonal planar arrangement.

The C's with lone pairs are sp³ and have a tetrahedral arrangement.

Here's more info on hybridization:

https://courses.lumenlearning.com/chemistryformajors/chapter/hybrid-atomic-orbitals/