In the following allylic radicals, identify the carbon where the new C― Br bond is most likely to form in the second propagation step.
(b)

Verified step by step guidance

1. Identify the structure of the allylic radical. An allylic radical is a radical located at the carbon atom adjacent to a double bond. This radical is stabilized by resonance.
2. Draw the resonance structures of the allylic radical. Resonance structures are different ways of arranging the electrons in a molecule that can help visualize the distribution of electron density.
3. Examine the resonance structures to determine which carbon atoms have the highest electron density. The carbon with the highest electron density is the most likely site for the formation of a new bond.
4. Consider the stability of the potential new C―Br bond. The bond is more likely to form at the carbon that results in the most stable product, often the one with the most substituted carbon.
5. Select the carbon atom where the new C―Br bond is most likely to form based on the resonance structures and stability considerations. This is typically the carbon that is most substituted or has the highest electron density in the resonance structures.

Key Concepts

Allylic Radical Stability

Allylic radicals are stabilized by resonance, which allows the unpaired electron to be delocalized over multiple atoms. This delocalization increases the stability of the radical, making allylic positions more reactive in radical reactions. Understanding this stability is crucial for predicting where new bonds will form.

Resonance Structures

Resonance structures are different ways of drawing the same molecule, showing the delocalization of electrons. In allylic radicals, resonance allows the radical to be spread over several carbon atoms, influencing the site of reactivity. Identifying resonance structures helps determine the most stable and reactive positions for bond formation.

Radical Propagation Steps

Radical reactions proceed through initiation, propagation, and termination steps. In the propagation step, radicals react with other molecules to form new radicals and products. Understanding the mechanism of propagation, especially in allylic systems, is essential for predicting where new bonds, such as C-Br, will form.