Question

Describe the ground-state electron configuration of the cyclopentadienyl cation and radical. Assuming each species is planar, would you expect it to be aromatic or antiaromatic?

Short answer

Question: Determine the ground-state electron configuration of the cyclopentadienyl cation and radical, and analyze whether these species are aromatic or antiaromatic. Answer: The ground-state electron configuration for the cyclopentadienyl cation (C5H5+) has 4 pi-electrons, making it antiaromatic. The cyclopentadienyl radical (C5H5•) has 5 pi-electrons, making it aromatic.

Step-by-step solution

Draw the structures of cyclopentadienyl cation and radical

Draw the planar structures of cyclopentadienyl cation (C5H5+) and cyclopentadienyl radical (C5H5•) with their five carbon atoms arranged in a cyclic form. The cation will have one positive charge, while the radical will have one unpaired electron.

Calculate the ground-state electron configuration

In both species, each carbon atom has a hybridization of sp2 with a double bond on alternate carbon atoms. Perform a pi-electron count as below: - Cyclopentadienyl cation (C5H5+): 5 carbon atoms with a total of 4 pi-electrons (one pair from each double bond) - Cyclopentadienyl radical (C5H5•): 5 carbon atoms with a total of 5 pi-electrons (one pair from each double bond + one unpaired electron)

Apply Hückel's rule to determine aromaticity

Hückel's rule states that a planar, cyclic compound with a continuous overlapping of p-orbitals will be aromatic if it has (4n+2) pi-electrons, where n is an integer (0, 1, 2,...), and antiaromatic if it has 4n pi-electrons. - Cyclopentadienyl cation (C5H5+) has 4 pi-electrons, which fits the rule for antiaromatic compounds (4n, n = 1). As a result, the cyclopentadienyl cation is antiaromatic. - Cyclopentadienyl radical (C5H5•) has 5 pi-electrons, which fits the rule for aromatic compounds (4n+2, n = 1). As a result, the cyclopentadienyl radical is aromatic. In conclusion, assuming each species is planar, the cyclopentadienyl cation is antiaromatic, while the cyclopentadienyl radical is aromatic.