Nucleophilic Substitution and Beta Elimination – SN1 SN2 E1 E2 Reactions

Substitution Elimination Reactions Tutorial Video SeriesOne of the more difficult topics covered in the standard Organic Chemistry 1 course involves Nucleophilic Substitution and Beta Elimination Reactions, designated: SN1 SN2 E1 E2.
My goal with this video series is to help you UNDERSTAND

SN1SN2 E1 E2 Organic Chemistry Cheat Sheet by Leah4Sci

SN1 SN2 E1 E2 Cheat Sheet

how to reason between the different reactions rather than having you memorize molecules and formulas that will leave you confused and guessing.

Think you’ve mastered it all? Jump right to my SN1 SN2 E1 E2  Practice Quiz!


Also, check out the printable/downloadable SN1 SN2 E1 E2 Cheat Sheet for quick reference and review.

Included in this series:

Video 1 – Introduction To Substitution And Elimination Reaction Analysis

Introduction to Nucleophilic Substitution and Beta Eliminatios Reactions tutorial videoMany students read ‘introduction’ and translate ‘skip this video’ I’m here to tell you NOT TO. The introductory video is under 2 minutes long, and my goal here is to give you an idea of how to approach substitution and elimination problems when asked to differentiate between them all.

Video 2 – SN1 SN2 E1 E2 Reactions Mechanism ReviewSN1 SN2 E1 E2 Reaction Mechanism Overview Video

This video will give you a quick overview/review of the individual reactions and mechanisms of SN1, SN2, E1, & E2 to prepare you for the detailed tutorials. This is great to watch as an overview before diving in, review in daily study, or review before quizzes/exams.

◊ 4 Components You Must Analyze ◊

When faced with a set of reactions conditions and asked to determine the type of substitution or elimination reactions, you cannot simply approach this with a set of memorized rules. Instead, you will have to analyze each aspect, one at a time, and find the reaction or reactions that best fit the given conditions. There are 4 major components to analyze prior to determining your reaction type. I will discuss each aspect in detail in its own video.

Component 1 – Alkyl Halide Carbon Chain Analysis

The type of carbon holding the leaving group is very important when determining between a ‘1’ type reaction, which undergoes a carbocation intermediate, or a ‘2’ type reaction which occurs in a single step.

You must analyze the chain as follows:

  • What is the degree of substitution of the carbon holding the leaving group?
  • Can a stable carbocation form?
  • How bulky are the nearby groups, and do they provide steric hindrance?
  • What is the availability and substitution of beta hydrogen atoms?

These questions are discussed in detail in the following video.

Video 3 – Alkyl Halide Carbon Chain Analysis

Alkyl halide carbon chain analysis video for substititutin and elimination reactions tutorial videoUnderstanding how the position of the leaving group impacts reactions will help you determine which reaction types are possible and which reactions to rule out.



Component 2 – Nucleophile Or Base and Strength Of Attacking Group

The attacking molecule in substitution or elimination reactions will be defined by the type of reaction that takes place. Meaning, if a molecule attacks a carbon forming a new bond and remaining attached to the chain, it has acted as a nucleophile. However, if instead the same molecule grabs a beta hydrogen atom without attaching itself to the parent molecule, it has acted as a base.
Many bases make good nucleophiles and many nucleophiles make decent bases. When analyzing a reaction it may be difficult to predict substiution or elimination by looking at just the attacker, instead you have to take everything into account. However the attacking molecule will help you determine between a ‘1’ type and a ‘2’ type reaction.

Video 4 – Nucleophilicity vs Basicity in Substitution Elimination Reactions Part 1

Nucleophile and Base Analysis for Substitution and Elimination Reactions Part 1 tutorial videoThis video helps you understand the similarities between nucleophiles and bases, as well as the major differences between the attacker in a ‘1’ type or ‘2’ type reaction (meaning SN1 E1 vs SN2 E2)

Once you have differentiated between the ‘1’ and ‘2’ type reactions, you want to refer to your starting molecule and solvent to determine if you will have substitution and elimination.

Video 5- Nucleophilicity vs Basiscity in Substitution Elimination Reactions Part 2

Nucleophile and Base Analysis for Substitution and Elimination Reactions Part 2 tutorial videoHowever, there are some attacking molecules that will easily help you differentiate between SN2 and E2.
In this video, you will learn there is a unique type of base, which I refer too as the ‘triple B’ for Big Bulky Base, which acts as a terrible nucleophile.
There are also some molecules that while weak in basicity actually make decent nucleophiles due to their polarizability.

Component 3 – Solvent Analysis: Polar Protic, Polar Aprotic, and Non-Polar

The type of solvent used in the reaction will also help you determine reaction type. While the ‘1’ type reactions, E1 and SN1 will typically occur simultaneously, solvent can help you distinguish between the ‘2’ type reactions E2 and SN2
There are 3 types of solvents that occur in organic chemistry reactions:

  • Polar Protic Solvents – These have polarity and H-bond donor groups
  • Polar Aprotic Solvents – Still polar, but no H-bond donor in the solvent molecule
  • Non-Polar Solvents – Hydrophobic solvents lacking polarity and the ability to H-bond

Video 6 – Polar Protic, Aprotic, and Non-Polar SolventsPolar Protic, Aprotic, and Non-Polar Solvents in Substitution and Elimination Reactions tutorial video

This video will help you understand understand what makes a solvent polar, and what makes a polar solvent protic or aprotic.


And Finally, Component 4 – Leaving Group

Video 7 – Leaving Groups Part 1

Leaving Groups in Substitution and Elimination Reactions Part 1 tutorial videoCan the group leave? Will the group leave?




Video 8 – Leaving Groups Part 2: Oxygen As A Leaving Group Using Tosylate And Mesylate

Oxygen As A Leaving Group Using Tosylate And Mesylate in Substitution & Elimination Reactions Tutorial VideoAnd figure out what to do when your leaving group Doesn’t WANT to leave




◊ You’ve got the Basics – Now Reactions ◊

SN1 – Unimolecular Nucleophilic Substitution

Video 9 – SN1 Reaction Rate and MechanismSN1 Reaction Rate and Mechanism - Unimolecular Nucleophilic Substitution Part 1 Tutorial Video

This video breaks down the reaction, rate, and step by step mechanism for the SN1 reactions including a few simple examples to help you follow along.



Video 10 – SN1 Reaction Mechanism Examples

SN1 Reaction Mechanism Examples of Unimolecular Substitution Part 2 Video Tutorial

As you work through this video pay attention to the logic, concepts, and especially patterns.



Video 11 – SN1 Reaction Mechanism with Hydride Shift and Carbocation RearrangementSN1 Reaction Mechanism with Hydride Shift and Carbocation Rearrangement Part 3 Tutorial Video

This video gives tricky examples involving less substituted carbocation intermediates followed by carbocation rearrangements and hydride shifts.



SN2 – Bimolecular Nucleophilic Substitution

Video 12 – SN2 Reaction Rate & Mechanism

SN2 Reaction Rate and Mechanism Bimolecular Substitution Part 1 Tutorial VideoThis video gives you a detailed overview of the SN2 reactions, reaction rate, step by step mechanism.

Pay special attention to the features that determine an SN2 reaction and the potential chirality of the final product.


Video 13 – SN2 Reaction Chirality & Mechanism

Comparing Between SN1 and SN2 Reactions


E1 – Unimolecular Beta Elimination

E2 – Bimolecular Beta Elimination

Having gone through this series, how do you feel about SN1/SN2 & E1/E2?

After watching the series, the best way to understand if you’ve fully mastered the questions is to Test yourself! Try my SN1 SN2 E1 E2  Practice Quiz! Also, check out the printable/downloadable SN1 SN2 E1 E2 Cheat Sheet for quick reference and review.

<– Back to the Organic Chemistry Syllabus Companion
to see what to study next!