The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.
h. Add an electron to the pentadienyl radical to give the pentadienyl anion. Which carbon atoms share the negative charge? Does this picture agree with the resonance picture?

Verified step by step guidance

1. Step 1: Understand the structure of the pentadienyl radical. The pentadienyl radical, H₂C=CH-CH=CH-CH₂·, is a conjugated system with alternating double and single bonds. The unpaired electron is delocalized over the three central carbon atoms (C2, C3, and C4) due to resonance.
2. Step 2: Add an electron to the pentadienyl radical. Adding an electron to the radical will pair with the unpaired electron, resulting in a pentadienyl anion. This anion now has a negative charge that is delocalized over the conjugated system.
3. Step 3: Draw the resonance structures of the pentadienyl anion. The negative charge is delocalized over the three central carbon atoms (C2, C3, and C4) through resonance. Write out the resonance structures to visualize how the negative charge shifts between these carbons.
4. Step 4: Analyze the resonance picture. The resonance structures show that the negative charge is shared among C2, C3, and C4. This delocalization stabilizes the anion and agrees with the resonance picture of the pentadienyl radical.
5. Step 5: Conclude the analysis. The negative charge in the pentadienyl anion is shared over the three central carbon atoms (C2, C3, and C4), and this picture is consistent with the resonance structures. This delocalization is a key feature of conjugated systems and contributes to the stability of the anion.

Key Concepts

Radicals and Anions

Radicals are species with unpaired electrons, making them highly reactive. In contrast, anions are negatively charged species that have gained an electron. The pentadienyl radical has an unpaired electron that can be stabilized by delocalization across multiple carbon atoms. When an electron is added to form the pentadienyl anion, the negative charge is distributed among the carbon atoms involved in the double bonds.

Delocalization of Electrons

Delocalization refers to the spreading of electrons across multiple atoms rather than being localized between two. In the case of the pentadienyl radical and anion, the unpaired electron and the added electron can be delocalized over the carbon atoms involved in the conjugated system. This delocalization stabilizes the radical and anion, allowing for resonance structures that depict the distribution of the negative charge.

Resonance Structures

Resonance structures are different ways of drawing a molecule that illustrate the delocalization of electrons. For the pentadienyl anion, resonance structures show how the negative charge can be shared among different carbon atoms. This concept helps in understanding the stability of the anion, as the actual structure is a hybrid of these resonance forms, reflecting the distribution of the negative charge across the molecule.