Organic Chemistry - Nucleophilic Aromatic Substitution (NAS) | 18.6Organic Chem

Chad presents a comprehensive lesson on nucleophilic aromatic substitution of aryl halides. Chad presents both possible mechanisms for this reaction: 1) Addition-Elimination and 2) Elimination-Addition (the Benzyne mechanism) and explains how you can tell which mechanism is more likely for a particular aryl halide. Addition Elimination Mechanism The Addition Elimination mechanism is named such as it begins with addition of the nucleophile at the benzene carbon atom where the halogen is attached. The intermediate formed is an anion which then undergoes subsequent elimination to restore aromaticity with the halogen leaving. Benzyne Mechanism (Elimination Addition Mechanism) The Elimination Addition, often called the Benzyne mechanism due to the unique benzyne intermediate in the reaction, reversed the order of steps beginning first with elimination followed addition. The elimination is akin to E2 elimination which temporarily results in a triple bond in the benzene ring, a benzyne intermediate. The nucleophile then adds to either of the sp carbon atoms of benzyne resulting in an anion intermediate which is subsequently protonated to yield the final product. I've created an organic chemistry page that organizes all my videos by chapter - just an easier way for you to watch my YouTube videos. Check it out at https://www.chadsprep.com/organic-chemistry-youtube 00:00 Lesson Introduction 00:47 Nucleophilic Aromatic Substitution 02:04 Addition-Elimination Mechanism 07:44 Elimination-Addition (Benzyne) Mechanism https://www.chadsprep.com/ #organicchemistry #organicchemistrytutorial #benzene