The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.
(g)

Verified step by step guidance

1. Step 1: Analyze the structure of each molecule or ion to determine the number of pi electrons in the ring system. Count the pi bonds and lone pairs that contribute to the conjugated system.
2. Step 2: Apply Hückel's rule for aromaticity, which states that a molecule is aromatic if it has (4n + 2) pi electrons, where n is a non-negative integer. If the molecule has 4n pi electrons, it is antiaromatic. If it does not meet either criterion, it is nonaromatic.
3. Step 3: For the first structure (leftmost), observe the conjugated ring system and count the pi electrons. Determine if the structure satisfies Hückel's rule or if it is antiaromatic or nonaromatic.
4. Step 4: For the second structure (middle), analyze the fused ring system. Count the total number of pi electrons in the conjugated system and check if it satisfies Hückel's rule for aromaticity or antiaromaticity.
5. Step 5: For the third structure (rightmost), consider the lone pair on the oxygen atom and its contribution to the conjugated system. Count the total pi electrons and determine if the molecule is aromatic, antiaromatic, or nonaromatic based on Hückel's rule.

Key Concepts

Aromaticity

Aromatic compounds are cyclic, planar molecules with a ring of p-orbitals that allows for delocalization of pi electrons. They must follow Hückel's rule, which states that a molecule is aromatic if it contains 4n + 2 pi electrons, where n is a non-negative integer. This delocalization contributes to the stability and unique reactivity of aromatic compounds.

Antiaromaticity

Antiaromatic compounds are also cyclic and planar but contain 4n pi electrons, leading to destabilization due to the presence of electron-electron repulsion in the ring. This results in a higher energy state compared to nonaromatic compounds. Antiaromatic compounds are generally less stable and more reactive than their aromatic counterparts.

Nonaromaticity

Nonaromatic compounds do not meet the criteria for aromaticity or antiaromaticity. They may be acyclic, lack planarity, or have an insufficient number of pi electrons in a ring structure. Nonaromatic compounds do not exhibit the special stability associated with aromatic compounds and can have varied reactivity depending on their structure.