Select the reaction "Benzylic oxidation." Observe the reaction several times. The animation uses oxygen \(\left(\mathrm{O}_{2}\right)\) as the initiator of the reaction, which also occurs in nature. One of the reasons for the common practice of packing organic foods over nitrogen \(\left(\mathrm{N}_{2}\right)\) is to avoid the reaction of \(\mathrm{O}_{2}\) with benzylic (and allylic) positions in natural products present in food. Draw each step of the reaction between \(\mathrm{O}_{2}\) and 2 -phenylpropane. Include a termination reaction. Label your steps as initiation, propagation, or termination.

In organic chemistry, free radical reactions play a significant role. These reactions involve molecules with unpaired electrons called radicals. Radicals are highly reactive.
They seek out other electrons to pair with, causing a chain reaction. This chain reaction is a sequence of reactions where a reactive intermediate generates another reactive intermediate.
This process continues until it is terminated.

The initiation step starts the chain reaction. This step involves the creation of radicals. In benzylic oxidation, the initiation step involves oxygen molecules.
Here, molecular oxygen \(\text{O}_2\) reacts with 2-phenylpropane to form a benzylic radical. Here’s the equation:
\(\text{C}_6\text{H}_5\text{CH}_2\text{CH}_3 + \text{O}_2 \rightarrow \text{C}_6 \text{H}_5 \text{CH}_{\cdot} \text{CH}_3 + \text{HO}_2^{\cdot}\).
The dot (•) shows an unpaired electron, indicating a free radical.

Propagation steps carry the reaction forward. In benzylic oxidation, there are two main propagation steps:
Propagation Step 1: The benzylic radical formed in the initiation step reacts with another oxygen molecule, creating a peroxy radical:
\(\text{C}_6\text{H}_5\text{CH}_{\cdot}\text{CH}_3 + \text{O}_2 \rightarrow \text{C}_6 \text{H}_5 \text{CH}(O_{\cdot}) \text{CH}_3\).
Propagation Step 2: In this step, the peroxy radical reacts with another 2-phenylpropane molecule.
This reaction leads to the formation of another benzylic radical and a hydroperoxide:
\(\text{C}_6\text{H}_5\text{CH}(O_{\cdot})\text{CH}_3 + \text{C}_6\text{H}_5\text{CH}_2\text{CH}_3 \rightarrow \text{C}_6 \text{H}_5 \text{CH}(O_2H) \text{CH}_3 + \text{C}_6 \text{H}_5 \text{CH}_{\cdot} \text{CH}_3\).

Termination reactions end the free radical chain reaction. This happens when two radicals combine to form a more stable product. In benzylic oxidation, if two benzylic radicals react,
they form a stable product depicted by:
\(2 \text{C}_6 \text{H}_5 \text{CH}_{\cdot} \text{CH}_3 \rightarrow \text{C}_6 \text{H}_5 \text{CH}_2 \text{CH}_3 + \text{C}_6 \text{H}_5 \text{C}(OH)(O)\text{CH}_3\).
By terminating the chain reaction, these steps ensure the reaction does not perpetuate indefinitely.

Understanding the mechanisms in organic chemistry helps us grasp how reactions occur. It explains the sequence of steps and intermediates through which reactants are converted to products.
Mechanisms give insight into the reaction’s kinetics and dynamics. By studying mechanisms, chemists can predict products and optimize reactions.
For example, in benzylic oxidation, the step-by-step study of initiation, propagation, and termination provides valuable information.
These mechanisms are crucial for developing new reactions and improving existing ones in chemical synthesis and industry.