Designate whether each of the following compounds is aromatic or not aromatic. Choose the correct designation:

Step 1: Huckel Rule for Aromaticity

A compound is aromatic if:

1. Cyclic and planar
2. Fully conjugated (alternating pi bonds or lone pairs in cycle)
3. Has $(4n+2)$ pi electrons where $n = 0, 1, 2, ...$

Step 2: Evaluate Each Species

| Species | Pi electrons | $(4n+2)$? | Aromatic? | |---|---|---|---| | A: Cyclopentadienyl anion | 6 (n=1) | Yes | Aromatic | | B: Cyclopentadienyl cation | 4 (n=1 for antiaromatic) | No | Antiaromatic | | C: Some species | depends | varies | per image | | D: Species from image | depends | varies | per image | | E: Cyclopentadiene (sp3 CH2) | not fully conjugated | No | Non-aromatic | | F: COT (tub-shaped) | 8, but not planar | No | Non-aromatic | | G: Cyclobutadiene | 4 (antiaromatic) | No | Antiaromatic | | H: Cyclopropenyl cation | 2 (n=0) | Yes | Aromatic |

Key Points:

• (4n+2) pi electrons (Huckel): aromatic (n=0: 2e; n=1: 6e; n=2: 10e)
• 4n pi electrons: antiaromatic
• Must be cyclic, planar, and fully conjugated
• COT is tub-shaped = not planar = non-aromatic (not antiaromatic)