(i) Classify the following molecules as aromatic, nonaromatic, or antiaromatic.
(ii) For aromatic molecules, solve for n in Hückel’s rule. For all other molecules, explain which rule of aromaticity is being broken.
(c)

Verified step by step guidance

1. Identify the molecule: The image shows a cycloheptatriene, which is a seven-membered ring with three alternating double bonds.
2. Determine the number of π electrons: Cycloheptatriene has 6 π electrons from the three double bonds.
3. Apply Hückel's rule: For a molecule to be aromatic, it must have (4n + 2) π electrons, where n is a non-negative integer. Check if 6 fits this formula.
4. Check planarity and cyclic nature: The molecule must be planar and cyclic for aromaticity. Cycloheptatriene is cyclic but not planar due to the presence of a non-conjugated sp3 hybridized carbon.
5. Classify the molecule: Since cycloheptatriene does not meet the planarity requirement, it is nonaromatic. It does not fulfill Hückel's rule due to the sp3 hybridized carbon disrupting conjugation.

Key Concepts

Aromaticity

Aromaticity refers to a property of cyclic compounds that exhibit enhanced stability due to the delocalization of π electrons. For a molecule to be classified as aromatic, it must be cyclic, planar, fully conjugated, and follow Hückel's rule, which states that the number of π electrons must equal 4n + 2, where n is a non-negative integer.

Hückel's Rule

Hückel's rule is a criterion used to determine the aromaticity of a compound. It states that a planar, cyclic molecule is aromatic if it contains 4n + 2 π electrons in its conjugated system. This rule helps in identifying aromatic compounds by calculating the total number of π electrons and checking if they fit the formula.

Anti-aromaticity

Anti-aromaticity is a property of cyclic compounds that are destabilized due to the presence of 4n π electrons, which leads to increased energy and instability. Unlike aromatic compounds, anti-aromatic compounds do not satisfy Hückel's rule and often exhibit significant reactivity and strain due to their unfavorable electronic configuration.