7.3 SN1 vs SN2 | Organic Chemistry

The video begins with an introduction to the study of SN1 and SN2 reactions, which have been covered in previous lessons. The focus of this lesson is to compare and contrast these two types of reactions, looking at substrate differences, nucleophiles, solvents, leaving group trends, and other distinctions. The presenter, Chad, aims to make science understandable and enjoyable, and he introduces his organic chemistry playlist that will be updated weekly throughout the 2020-21 school year. The video also touches on the reactivity of sp2 halides, explaining why they do not undergo SN1 or SN2 reactions due to the stability of the resulting carbocations and steric hindrance.

This paragraph delves into the criteria used to differentiate between SN1 and SN2 reactions. It emphasizes the importance of the nucleophile, substrate, and solvent in determining the reaction type. The video provides a table summarizing the reactivity of different substrates, the strength of nucleophiles, and the preference for polar aprotic solvents in SN2 reactions versus polar protic solvents in SN1 reactions. It also discusses the common leaving group trend for both reactions and the possibility of rearrangements in SN1 reactions but not in SN2. Stereoselectivity is highlighted, with SN2 reactions resulting in inversion at chiral centers and SN1 potentially leading to racemization.

The presenter walks through several examples to illustrate how to identify whether a reaction is an SN1 or SN2 based on the nucleophile, substrate, and solvent. The examples include identifying the leaving group, determining if the nucleophile is strong or weak, and assessing the substrate's reactivity. The video explains that a strong nucleophile typically indicates an SN2 reaction, while a weak nucleophile points to an SN1 reaction. It also covers solvolysis reactions and the importance of drawing out the carbocation intermediate to check for rearrangements, especially in the case of secondary and tertiary substrates.

The video presents more complex examples that involve primary substrates stabilized by resonance, leading to SN1 reactions despite the general rule that primary substrates do not typically undergo SN1. It also discusses the possibility of multiple substitution locations due to resonance stabilization. The presenter explains the formation of enantiomers when substitution occurs at a chiral center and the unique scenario where a weak nucleophile can attack at two different locations because of resonance stabilization. The importance of drawing out both resonance structures is emphasized for a complete understanding.

The final paragraph wraps up the lesson with a couple more examples, including one with a neutral but strong nucleophile that leads to an SN2 reaction. It highlights the unique outcome of a product with a positive formal charge when the nucleophile cannot be deprotonated. The presenter encourages viewers to like, share, and subscribe for more content and to ask questions in the comments. He also mentions the availability of study guides, quizzes, chapter tests, and practice final exams in his premium course on Chad's Prep website.