The lecture series provides a foundational understanding of radical reactions in organic chemistry. 

Fundamental Radical Mechanisms and Radical Chlorination

The lecture videos starta with fundamental definitions and concepts. We learn that radicals are atoms, molecules, or ions characterized by an unpaired electron in their electronic configuration and explore their bonding patterns and stability trends, noting that carbon radical stability mirrors that of carbocations due to hyperconjugation. The lectures will also cover the curved arrow patterns for one-electron motions, known as fish hook arrows, which are crucial for depicting resonance structures and radical mechanisms. A significant portion will be dedicated to the six common patterns in radical mechanisms: homolytic cleavage, addition to a pi bond, hydrogen atom abstraction, halogen atom abstraction, elimination, and coupling reactions, contrasting them with ionic mechanisms by highlighting that radical reactions do not undergo rearrangements. Finally, the first video will illustrate these concepts through a detailed examination of the chlorination of methane, explaining its progression through a radical chain mechanism with its three distinct stages: initiation, propagation, and termination.

Thermodynamic Considerations for Radical Halogenation Reactions

Building on the basics, the second video delves into thermodynamic considerations for radical halogenation reactions, demonstrating how bond dissociation energies (BDEs) can be used to predict reactivity and regioselectivity. It will clarify why only radical chlorination and bromination reactions are synthetically viable, excluding fluorination (too explosive) and iodination (thermodynamically unfavorable). You will also gain an understanding of the origins of reactivity and regioselectivity in these reactions, specifically noting that the hydrogen abstraction step is typically rate-determining due to the strength of the C-H bond. The Hammond postulate will be introduced as a key tool to explain how the nature of the transition state influences selectivity, emphasizing that radical brominations are slower but more regioselective than chlorinations. The lectures will conclude this segment by detailing the stereochemical outcomes of radical halogenations, explaining why these reactions are non-stereoselective and often result in racemic mixtures, particularly when new chiral centers are formed or when halogenating at existing chiral centers, due to the trigonal planar nature of the intermediate carbon radical.

Allylic Bromination and Radical Hydrobromination 

The final video expands the discussion to more specific radical reactions, beginning with allylic bromination. You will learn about the weakness of allylic C-H bonds due to resonance stabilization of the resulting radical and the pitfalls of using Br2 as a brominating agent, which can lead to competing ionic addition reactions. The solution, using NBS (N-bromosuccinimide), will be explored in detail, including its radical chain mechanism that keeps Br2 concentration low to favor radical pathways. Additionally, the video will cover radical hydrobromination, also known as anti-Markovnikov hydrohalogenation. This section will explain the mechanism behind the anti-Markovnikov addition of HBr across a pi bond in the presence of peroxides, emphasizing how the bromine radical preferentially adds to the less substituted carbon to form the more stable carbon radical intermediate. Similar to other radical halogenations, you will learn to predict the major and minor products, including stereochemical outcomes, recognizing that both allylic bromination and radical hydrobromination are not stereoselective and can lead to a mixture of constitutional isomers and stereoisomers.

Student Learning Outcomes

Based on the lecture videos, by the end of the series, you should be able to achieve the following learning outcomes:

• Define radicals as atoms, molecules, or ions with an unpaired electron. 

• Predict carbon radical stability.

• Master curved arrow patterns for one-electron motions using fish hook arrows (single barbed arrows) to depict the motion of one electron.

• Identify and apply the six common patterns in radical mechanism. Distinguish these from ionic mechanisms, noting that radical reactions do not undergo rearrangements.

• Propose radical chain mechanisms.

• Utilize bond dissociation energies (BDEs) to predict reactivity and regioselectivity in radical halogenations.

• Explain the origins of reactivity and regioselectivity in radical halogenations. 

• Predict stereochemical outcomes of radical halogenations. 

• Explain the weakness of allylic C-H bonds due to resonance stabilization of the resulting radical. Identify the pitfalls of using Br2 as a brominating agent and explain why NBS (N-bromosuccinimide) is used instead to keep Br2 concentration low and favor radical pathways. 

• Predict product mixtures from allylic bromination, including constitutional isomers, when resonance leads to radical character at multiple carbons.

• Propose the radical chain mechanism for the anti-Markovnikov addition of HBr across a pi bond in the presence of peroxides. Like other radical halogenations, predict the major and minor products, including stereochemical outcomes, recognizing that this reaction is also not stereoselective.

• Predict major and minor products, including stereochemical outcomes, for allylic brominations and radical hydrobrominations.