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SN1/SN2/E1/E2 Decision
Deciding SN1/SN2/E1/E2 (4) – The Temperature
Last updated: November 29th, 2022 |
The Quick N’ Dirty Guide To Determining SN1/SN2/E1/E2, Part 4 : The Role of Temperature
The Quick N’ Dirty Guide to SN1/SN2/E1/E2 involves analyzing four key variables, in order of their importance.
- Substrate (first article)
- Base/Nucleophile (second article)
- Solvent (previous article)
- Temperature (this article)
Today, we’ll address the final variable to consider: the temperature.
If you’ve been following so far, you may have noticed that by this point we should be able to differentiate all cases where SN2 is favored over E2 (and vice versa) but are still left with this dilemma: when a carbocation is formed, how do we determine whether SN1 or E1 products are favored?
That’s where the temperature will help us determine whether the reaction is SN1 or E1.
If you need a refresher on these reactions, read these and come back:
How Do We Determine Whether SN1 versus E1 Will Dominate Once A Carbocation Has Formed?
First of all, note that the first step of the SN1 and E1 reactions is the same: loss of a leaving group to give a carbocation. Since both of these reactions proceed via the same intermediate, in practice a mixture of both SN1 and E1 products will be found whenever the reaction proceeds through a carbocation [where possible].
Given that, however, we would still like to have a rule of thumb that tells us what type of product should be the major product in most cases.
Generally speaking, SN1 products tend to predominate over E1 products at lower temperatures.
However, recall that elimination reactions are favored by heat (See article: Elimination Reactions Are Favored By Heat)
In cases where substitution reactions and elimination reactions are in competition with each other, increasing the temperature tends to increase the amount of elimination products produced.
Here is a representative example:
- Loss of bromide ion from the tertiary alkyl bromide substrate leads to the formation of a tertiary carbocation [stable, hence no rearrangement].
- At low temperatures, the SN1 pathway (above) will dominate; the carbocation is attacked by CH3OH, followed by loss of proton to give the ether product.
- The bottom pathway (E1) – removal of hydrogen from the carbon adjacent to the carbocation – will be minor at low temperature [note the formation of the more substituted alkene here – Zaitsev’s rule in action].
- However, as temperature is increased, the amount of elimination relative to substitution should gradually increase.
This leads to the following Quick N’ Dirty rule of thumb.
If “Heat” Is Noted, The Reaction Will Favor E1 Over SN1
Quick N’ Dirty Rule #6:
- When carbocations are formed, at low temperatures, the SN1 pathway will dominate over the E1 pathway.
- At higher temperatures, more E1 products will be formed.
(Note: before applying these reaction patterns to the substrate, make sure to examine the carbocation that is formed. If a more stable carbocation can be formed through a hydride or alkyl shift, do this rearrangement first!)
Let’s go back to the examples we’ve been working on.
- The third case – addition of H2SO4 to a tertiary alcohol – is a case where a carbocation is formed in the absence of a good nucleophile [See post – Elimination of Alcohols With Acid]. The fact that heat is being applied helps to tip the balance even further toward E1 being dominant over SN1.
- In the fourth example we have a tertiary halide [which will form a stable carbocation] in a polar protic solvent [will help to stabilize the intermediate carbocation] and heat is not indicated.
- Therefore using Quick N’ Dirty Rule #6, we can say that SN1 products will dominate. [E1 products will form as well, but they will not be the major products].
This is truly a Quick N’ Dirty rule. It is not applied evenly and there are plenty of exceptions. Your mileage will vary widely. [Note 1]
In the next post we’ll summarize all the Quick N’ Dirty Rules for determining whether a reaction goes SN1/SN2/E1/E2.
Next Post: Wrapup of the Quick N’ Dirty Guide
———–END QUICK N’ DIRTY DISCUSSION ————-
Notes
Related Articles
- Wrapup: The Quick N’ Dirty Guide To SN1/SN2/E1/E2
- The SN1 Mechanism
- The E1 Reaction
- Comparing the E1 vs SN1 Reactions
- Elimination Reactions Are Favored By Heat
- Deciding SN1/SN2/E1/E2 (1) – The Substrate
- Deciding SN1/SN2/E1/E2 (2) – The Nucleophile/Base
- Deciding SN1/SN2/E1/E2 (3) – The Solvent
- SN1 SN2 E1 E2 Practice Problems (MOC Membership)
Note 1. I am annoyed by the lack of hard data available when making pronouncements about the SN1/SN2/E1/E2 decision. Wohler’s quote about the “monstrous and boundless thicket… into which one may well dread to enter” seems appropriate here. I would love to see the control experiments with various substrates run under identical sets of conditions that clearly delineate the impact of each variable. I have not seen this. Any undergraduate labs out there with a desire for performing this valuable public service?
Note 2. A final note/editorial.
One Difference Between “Real ” Chemistry and “Exam Question” Chemistry
The post above is not so much about understanding some facet of organic chemistry as it is about how to answer some arbitrary question from a textbook or exam. For the purpose of understanding organic chemistry, it’s enough to know that heat favors elimination reactions. For the purpose of knowing how to answer a particular kind of question on an exam, it will of course depend on the examiner. There are wide variations. However, I will share with you one common observation that I’ve seen in 2.5 years of seeing exams from all over the country.
First, background. In the laboratory, it is extremely common to heat reactions to get them to go at a reasonable speed, such as in this example [from March’s Advanced Organic Chemistry 5th ed; Cooper, K.A. et. al. J. Chem. Soc. 1948, 2038:]
However, on an exam, instructors – for various reasons, including a well-intentioned desire not to overwhelm the student – will often omit some of the data. For exam purposes, if the above reaction were written as a question it will often look like this:
Note how “heat” has been omitted, which is in accord with the principle of least effort. The expected answer in this instance would be t-BuOH, the product of an SN1 reaction. Depending on the question wording, some instructors will also insist that the E1 product be drawn as well.
Here’s the observation I see in many (but certainly not all) courses. If the word “heat” is written in the exam question, it is often a clue from the instructor that an elimination is to take place. In the following reaction, for example, the question would point to elimination (2-methyl propene) being the major product.
If you are a student and your goal is to answer a particular type of question on an exam correctly, I advise you to double check this issue with your instructor and get their answer on it. There is tremendous inconsistency in this practice nationwide.
Struggling with SN1/SN2/E1/E2? Our Org 1 Summary Sheets (PDF) contain a full-page flowchart on deciding SN1/SN2/E1/E2, as well as two more pages summarizing substitution and elimination reactions, in addition to many other Org 1 topics.
Check them out now!
00 General Chemistry Review
01 Bonding, Structure, and Resonance
- How Do We Know Methane (CH4) Is Tetrahedral?
- Hybrid Orbitals and Hybridization
- How To Determine Hybridization: A Shortcut
- Orbital Hybridization And Bond Strengths
- Sigma bonds come in six varieties: Pi bonds come in one
- A Key Skill: How to Calculate Formal Charge
- Partial Charges Give Clues About Electron Flow
- The Four Intermolecular Forces and How They Affect Boiling Points
- 3 Trends That Affect Boiling Points
- How To Use Electronegativity To Determine Electron Density (and why NOT to trust formal charge)
- Introduction to Resonance
- How To Use Curved Arrows To Interchange Resonance Forms
- Evaluating Resonance Forms (1) - The Rule of Least Charges
- How To Find The Best Resonance Structure By Applying Electronegativity
- Evaluating Resonance Structures With Negative Charges
- Evaluating Resonance Structures With Positive Charge
- Exploring Resonance: Pi-Donation
- Exploring Resonance: Pi-acceptors
- In Summary: Evaluating Resonance Structures
- Drawing Resonance Structures: 3 Common Mistakes To Avoid
- How to apply electronegativity and resonance to understand reactivity
- Bond Hybridization Practice
- Structure and Bonding Practice Quizzes
- Resonance Structures Practice
02 Acid Base Reactions
- Introduction to Acid-Base Reactions
- Acid Base Reactions In Organic Chemistry
- The Stronger The Acid, The Weaker The Conjugate Base
- Walkthrough of Acid-Base Reactions (3) - Acidity Trends
- Five Key Factors That Influence Acidity
- Acid-Base Reactions: Introducing Ka and pKa
- How to Use a pKa Table
- The pKa Table Is Your Friend
- A Handy Rule of Thumb for Acid-Base Reactions
- Acid Base Reactions Are Fast
- pKa Values Span 60 Orders Of Magnitude
- How Protonation and Deprotonation Affect Reactivity
- Acid Base Practice Problems
03 Alkanes and Nomenclature
- Meet the (Most Important) Functional Groups
- Condensed Formulas: Deciphering What the Brackets Mean
- Hidden Hydrogens, Hidden Lone Pairs, Hidden Counterions
- Don't Be Futyl, Learn The Butyls
- Primary, Secondary, Tertiary, Quaternary In Organic Chemistry
- Branching, and Its Affect On Melting and Boiling Points
- The Many, Many Ways of Drawing Butane
- Wedge And Dash Convention For Tetrahedral Carbon
- Common Mistakes in Organic Chemistry: Pentavalent Carbon
- Table of Functional Group Priorities for Nomenclature
- Summary Sheet - Alkane Nomenclature
- Organic Chemistry IUPAC Nomenclature Demystified With A Simple Puzzle Piece Approach
- Boiling Point Quizzes
- Organic Chemistry Nomenclature Quizzes
04 Conformations and Cycloalkanes
- Staggered vs Eclipsed Conformations of Ethane
- Conformational Isomers of Propane
- Newman Projection of Butane (and Gauche Conformation)
- Introduction to Cycloalkanes (1)
- Geometric Isomers In Small Rings: Cis And Trans Cycloalkanes
- Calculation of Ring Strain In Cycloalkanes
- Cycloalkanes - Ring Strain In Cyclopropane And Cyclobutane
- Cyclohexane Conformations
- Cyclohexane Chair Conformation: An Aerial Tour
- How To Draw The Cyclohexane Chair Conformation
- The Cyclohexane Chair Flip
- The Cyclohexane Chair Flip - Energy Diagram
- Substituted Cyclohexanes - Axial vs Equatorial
- Ranking The Bulkiness Of Substituents On Cyclohexanes: "A-Values"
- The Ups and Downs of Cyclohexanes
- Cyclohexane Chair Conformation Stability: Which One Is Lower Energy?
- Fused Rings - Cis-Decalin and Trans-Decalin
- Naming Bicyclic Compounds - Fused, Bridged, and Spiro
- Bredt's Rule (And Summary of Cycloalkanes)
- Newman Projection Practice
- Cycloalkanes Practice Problems
05 A Primer On Organic Reactions
- The Most Important Question To Ask When Learning a New Reaction
- The 4 Major Classes of Reactions in Org 1
- Learning New Reactions: How Do The Electrons Move?
- How (and why) electrons flow
- The Third Most Important Question to Ask When Learning A New Reaction
- 7 Factors that stabilize negative charge in organic chemistry
- 7 Factors That Stabilize Positive Charge in Organic Chemistry
- Common Mistakes: Formal Charges Can Mislead
- Nucleophiles and Electrophiles
- Curved Arrows (for reactions)
- Curved Arrows (2): Initial Tails and Final Heads
- Nucleophilicity vs. Basicity
- The Three Classes of Nucleophiles
- What Makes A Good Nucleophile?
- What makes a good leaving group?
- 3 Factors That Stabilize Carbocations
- Equilibrium and Energy Relationships
- What's a Transition State?
- Hammond's Postulate
- Grossman's Rule
- Draw The Ugly Version First
- Learning Organic Chemistry Reactions: A Checklist (PDF)
- Introduction to Addition Reactions
- Introduction to Elimination Reactions
- Introduction to Free Radical Substitution Reactions
- Introduction to Oxidative Cleavage Reactions
06 Free Radical Reactions
- Bond Dissociation Energies = Homolytic Cleavage
- Free Radical Reactions
- 3 Factors That Stabilize Free Radicals
- What Factors Destabilize Free Radicals?
- Bond Strengths And Radical Stability
- Free Radical Initiation: Why Is "Light" Or "Heat" Required?
- Initiation, Propagation, Termination
- Monochlorination Products Of Propane, Pentane, And Other Alkanes
- Selectivity In Free Radical Reactions
- Selectivity in Free Radical Reactions: Bromination vs. Chlorination
- Halogenation At Tiffany's
- Allylic Bromination
- Bonus Topic: Allylic Rearrangements
- In Summary: Free Radicals
- Synthesis (2) - Reactions of Alkanes
- Free Radicals Practice Quizzes
07 Stereochemistry and Chirality
- Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers
- How To Draw The Enantiomer Of A Chiral Molecule
- How To Draw A Bond Rotation
- Introduction to Assigning (R) and (S): The Cahn-Ingold-Prelog Rules
- Assigning Cahn-Ingold-Prelog (CIP) Priorities (2) - The Method of Dots
- Enantiomers vs Diastereomers vs The Same? Two Methods For Solving Problems
- Assigning R/S To Newman Projections (And Converting Newman To Line Diagrams)
- How To Determine R and S Configurations On A Fischer Projection
- The Meso Trap
- Optical Rotation, Optical Activity, and Specific Rotation
- Optical Purity and Enantiomeric Excess
- What's a Racemic Mixture?
- Chiral Allenes And Chiral Axes
- On Cats, Part 4: Enantiocats
- On Cats, Part 6: Stereocenters
- Stereochemistry Practice Problems and Quizzes
08 Substitution Reactions
- Introduction to Nucleophilic Substitution Reactions
- Walkthrough of Substitution Reactions (1) - Introduction
- Two Types of Nucleophilic Substitution Reactions
- The SN2 Mechanism
- Why the SN2 Reaction Is Powerful
- The SN1 Mechanism
- The Conjugate Acid Is A Better Leaving Group
- Comparing the SN1 and SN2 Reactions
- Polar Protic? Polar Aprotic? Nonpolar? All About Solvents
- Steric Hindrance is Like a Fat Goalie
- Common Blind Spot: Intramolecular Reactions
- The Conjugate Base is Always a Stronger Nucleophile
- Substitution Practice - SN1
- Substitution Practice - SN2
09 Elimination Reactions
- Elimination Reactions (1): Introduction And The Key Pattern
- Elimination Reactions (2): The Zaitsev Rule
- Elimination Reactions Are Favored By Heat
- Two Elimination Reaction Patterns
- The E1 Reaction
- The E2 Mechanism
- E1 vs E2: Comparing the E1 and E2 Reactions
- Antiperiplanar Relationships: The E2 Reaction and Cyclohexane Rings
- Bulky Bases in Elimination Reactions
- Comparing the E1 vs SN1 Reactions
- Elimination (E1) Reactions With Rearrangements
- E1cB - Elimination (Unimolecular) Conjugate Base
- Elimination (E1) Practice Problems And Solutions
- Elimination (E2) Practice Problems and Solutions
10 Rearrangements
11 SN1/SN2/E1/E2 Decision
- Identifying Where Substitution and Elimination Reactions Happen
- Deciding SN1/SN2/E1/E2 (1) - The Substrate
- Deciding SN1/SN2/E1/E2 (2) - The Nucleophile/Base
- Deciding SN1/SN2/E1/E2 (3) - The Solvent
- Deciding SN1/SN2/E1/E2 (4) - The Temperature
- Wrapup: The Quick N' Dirty Guide To SN1/SN2/E1/E2
- Alkyl Halide Reaction Map And Summary
- SN1 SN2 E1 E2 Practice Problems
12 Alkene Reactions
- E and Z Notation For Alkenes (+ Cis/Trans)
- Alkene Stability
- Addition Reactions: Elimination's Opposite
- Selective vs. Specific
- Regioselectivity In Alkene Addition Reactions
- Stereoselectivity In Alkene Addition Reactions: Syn vs Anti Addition
- Hydrohalogenation of Alkenes and Markovnikov's Rule
- Hydration of Alkenes With Aqueous Acid
- Rearrangements in Alkene Addition Reactions
- Addition Pattern #1: The "Carbocation Pathway"
- Halogenation of Alkenes and Halohydrin Formation
- Oxymercuration Demercuration of Alkenes
- Alkene Addition Pattern #2: The "Three-Membered Ring" Pathway
- Hydroboration Oxidation of Alkenes
- m-CPBA (meta-chloroperoxybenzoic acid)
- OsO4 (Osmium Tetroxide) for Dihydroxylation of Alkenes
- Palladium on Carbon (Pd/C) for Catalytic Hydrogenation
- Cyclopropanation of Alkenes
- Alkene Addition Pattern #3: The "Concerted" Pathway
- A Fourth Alkene Addition Pattern - Free Radical Addition
- Alkene Reactions: Ozonolysis
- Summary: Three Key Families Of Alkene Reaction Mechanisms
- Synthesis (4) - Alkene Reaction Map, Including Alkyl Halide Reactions
- Alkene Reactions Practice Problems
13 Alkyne Reactions
- Acetylides from Alkynes, And Substitution Reactions of Acetylides
- Partial Reduction of Alkynes With Lindlar's Catalyst or Na/NH3 To Obtain Cis or Trans Alkenes
- Hydroboration and Oxymercuration of Alkynes
- Alkyne Reaction Patterns - Hydrohalogenation - Carbocation Pathway
- Alkyne Halogenation: Bromination, Chlorination, and Iodination of Alkynes
- Alkyne Reactions - The "Concerted" Pathway
- Alkenes To Alkynes Via Halogenation And Elimination Reactions
- Alkynes Are A Blank Canvas
- Synthesis (5) - Reactions of Alkynes
- Alkyne Reactions Practice Problems With Answers
14 Alcohols, Epoxides and Ethers
- Alcohols - Nomenclature and Properties
- Alcohols Can Act As Acids Or Bases (And Why It Matters)
- Alcohols - Acidity and Basicity
- The Williamson Ether Synthesis
- Ethers From Alkenes, Tertiary Alkyl Halides and Alkoxymercuration
- Alcohols To Ethers via Acid Catalysis
- Cleavage Of Ethers With Acid
- Epoxides - The Outlier Of The Ether Family
- Opening of Epoxides With Acid
- Epoxide Ring Opening With Base
- Making Alkyl Halides From Alcohols
- Tosylates And Mesylates
- PBr3 and SOCl2
- Elimination Reactions of Alcohols
- Elimination of Alcohols To Alkenes With POCl3
- Alcohol Oxidation: "Strong" and "Weak" Oxidants
- Demystifying The Mechanisms of Alcohol Oxidations
- Protecting Groups For Alcohols
- Thiols And Thioethers
- Calculating the oxidation state of a carbon
- Oxidation and Reduction in Organic Chemistry
- Oxidation Ladders
- SOCl2 Mechanism For Alcohols To Alkyl Halides: SN2 versus SNi
- Alcohol Reactions Roadmap (PDF)
- Alcohol Reaction Practice Problems
- Epoxide Reaction Quizzes
- Oxidation and Reduction Practice Quizzes
15 Organometallics
- What's An Organometallic?
- Formation of Grignard and Organolithium Reagents
- Organometallics Are Strong Bases
- Reactions of Grignard Reagents
- Protecting Groups In Grignard Reactions
- Synthesis Problems Involving Grignard Reagents
- Grignard Reactions And Synthesis (2)
- Organocuprates (Gilman Reagents): How They're Made
- Gilman Reagents (Organocuprates): What They're Used For
- The Heck, Suzuki, and Olefin Metathesis Reactions (And Why They Don't Belong In Most Introductory Organic Chemistry Courses)
- Reaction Map: Reactions of Organometallics
- Grignard Practice Problems
16 Spectroscopy
- Degrees of Unsaturation (or IHD, Index of Hydrogen Deficiency)
- Conjugation And Color (+ How Bleach Works)
- Introduction To UV-Vis Spectroscopy
- UV-Vis Spectroscopy: Absorbance of Carbonyls
- UV-Vis Spectroscopy: Practice Questions
- Bond Vibrations, Infrared Spectroscopy, and the "Ball and Spring" Model
- Infrared Spectroscopy: A Quick Primer On Interpreting Spectra
- IR Spectroscopy: 4 Practice Problems
- 1H NMR: How Many Signals?
- Homotopic, Enantiotopic, Diastereotopic
- Diastereotopic Protons in 1H NMR Spectroscopy: Examples
- C13 NMR - How Many Signals
- Liquid Gold: Pheromones In Doe Urine
- Natural Product Isolation (1) - Extraction
- Natural Product Isolation (2) - Purification Techniques, An Overview
- Structure Determination Case Study: Deer Tarsal Gland Pheromone
17 Dienes and MO Theory
- What To Expect In Organic Chemistry 2
- Are these molecules conjugated?
- Conjugation And Resonance In Organic Chemistry
- Bonding And Antibonding Pi Orbitals
- Molecular Orbitals of The Allyl Cation, Allyl Radical, and Allyl Anion
- Pi Molecular Orbitals of Butadiene
- Reactions of Dienes: 1,2 and 1,4 Addition
- Thermodynamic and Kinetic Products
- More On 1,2 and 1,4 Additions To Dienes
- s-cis and s-trans
- The Diels-Alder Reaction
- Cyclic Dienes and Dienophiles in the Diels-Alder Reaction
- Stereochemistry of the Diels-Alder Reaction
- Exo vs Endo Products In The Diels Alder: How To Tell Them Apart
- HOMO and LUMO In the Diels Alder Reaction
- Why Are Endo vs Exo Products Favored in the Diels-Alder Reaction?
- Diels-Alder Reaction: Kinetic and Thermodynamic Control
- The Retro Diels-Alder Reaction
- The Intramolecular Diels Alder Reaction
- Regiochemistry In The Diels-Alder Reaction
- The Cope and Claisen Rearrangements
- Electrocyclic Reactions
- Electrocyclic Ring Opening And Closure (2) - Six (or Eight) Pi Electrons
- Diels Alder Practice Problems
- Molecular Orbital Theory Practice
18 Aromaticity
- Introduction To Aromaticity
- Rules For Aromaticity
- Huckel's Rule: What Does 4n+2 Mean?
- Aromatic, Non-Aromatic, or Antiaromatic? Some Practice Problems
- Antiaromatic Compounds and Antiaromaticity
- The Pi Molecular Orbitals of Benzene
- The Pi Molecular Orbitals of Cyclobutadiene
- Frost Circles
- Aromaticity Practice Quizzes
19 Reactions of Aromatic Molecules
- Electrophilic Aromatic Substitution: Introduction
- Activating and Deactivating Groups In Electrophilic Aromatic Substitution
- Electrophilic Aromatic Substitution - The Mechanism
- Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution
- Understanding Ortho, Para, and Meta Directors
- Why are halogens ortho- para- directors?
- Disubstituted Benzenes: The Strongest Electron-Donor "Wins"
- Electrophilic Aromatic Substitutions (1) - Halogenation of Benzene
- Electrophilic Aromatic Substitutions (2) - Nitration and Sulfonation
- EAS Reactions (3) - Friedel-Crafts Acylation and Friedel-Crafts Alkylation
- Intramolecular Friedel-Crafts Reactions
- Nucleophilic Aromatic Substitution (NAS)
- Nucleophilic Aromatic Substitution (2) - The Benzyne Mechanism
- Reactions on the "Benzylic" Carbon: Bromination And Oxidation
- The Wolff-Kishner, Clemmensen, And Other Carbonyl Reductions
- More Reactions on the Aromatic Sidechain: Reduction of Nitro Groups and the Baeyer Villiger
- Aromatic Synthesis (1) - "Order Of Operations"
- Synthesis of Benzene Derivatives (2) - Polarity Reversal
- Aromatic Synthesis (3) - Sulfonyl Blocking Groups
- Birch Reduction
- Synthesis (7): Reaction Map of Benzene and Related Aromatic Compounds
- Aromatic Reactions and Synthesis Practice
- Electrophilic Aromatic Substitution Practice Problems
20 Aldehydes and Ketones
- What's The Alpha Carbon In Carbonyl Compounds?
- Nucleophilic Addition To Carbonyls
- Aldehydes and Ketones: 14 Reactions With The Same Mechanism
- Sodium Borohydride (NaBH4) Reduction of Aldehydes and Ketones
- Grignard Reagents For Addition To Aldehydes and Ketones
- Wittig Reaction
- Hydrates, Hemiacetals, and Acetals
- Imines - Properties, Formation, Reactions, and Mechanisms
- All About Enamines
- Breaking Down Carbonyl Reaction Mechanisms: Reactions of Anionic Nucleophiles (Part 2)
- Aldehydes Ketones Reaction Practice
21 Carboxylic Acid Derivatives
- Nucleophilic Acyl Substitution (With Negatively Charged Nucleophiles)
- Addition-Elimination Mechanisms With Neutral Nucleophiles (Including Acid Catalysis)
- Basic Hydrolysis of Esters - Saponification
- Transesterification
- Proton Transfer
- Fischer Esterification - Carboxylic Acid to Ester Under Acidic Conditions
- Lithium Aluminum Hydride (LiAlH4) For Reduction of Carboxylic Acid Derivatives
- LiAlH[Ot-Bu]3 For The Reduction of Acid Halides To Aldehydes
- Di-isobutyl Aluminum Hydride (DIBAL) For The Partial Reduction of Esters and Nitriles
- Amide Hydrolysis
- Thionyl Chloride (SOCl2)
- Diazomethane (CH2N2)
- Carbonyl Chemistry: Learn Six Mechanisms For the Price Of One
- Making Music With Mechanisms (PADPED)
- Carboxylic Acid Derivatives Practice Questions
22 Enols and Enolates
- Keto-Enol Tautomerism
- Enolates - Formation, Stability, and Simple Reactions
- Kinetic Versus Thermodynamic Enolates
- Aldol Addition and Condensation Reactions
- Reactions of Enols - Acid-Catalyzed Aldol, Halogenation, and Mannich Reactions
- Claisen Condensation and Dieckmann Condensation
- Decarboxylation
- The Malonic Ester and Acetoacetic Ester Synthesis
- The Michael Addition Reaction and Conjugate Addition
- The Robinson Annulation
- Haloform Reaction
- The Hell–Volhard–Zelinsky Reaction
- Enols and Enolates Practice Quizzes
23 Amines
- The Amide Functional Group: Properties, Synthesis, and Nomenclature
- Basicity of Amines And pKaH
- 5 Key Basicity Trends of Amines
- The Mesomeric Effect And Aromatic Amines
- Nucleophilicity of Amines
- Alkylation of Amines (Sucks!)
- Reductive Amination
- The Gabriel Synthesis
- Some Reactions of Azides
- The Hofmann Elimination
- The Hofmann and Curtius Rearrangements
- The Cope Elimination
- Protecting Groups for Amines - Carbamates
- The Strecker Synthesis of Amino Acids
- Introduction to Peptide Synthesis
- Reactions of Diazonium Salts: Sandmeyer and Related Reactions
- Amine Practice Questions
24 Carbohydrates
- D and L Notation For Sugars
- Pyranoses and Furanoses: Ring-Chain Tautomerism In Sugars
- What is Mutarotation?
- Reducing Sugars
- The Big Damn Post Of Carbohydrate-Related Chemistry Definitions
- The Haworth Projection
- Converting a Fischer Projection To A Haworth (And Vice Versa)
- Reactions of Sugars: Glycosylation and Protection
- The Ruff Degradation and Kiliani-Fischer Synthesis
- Isoelectric Points of Amino Acids (and How To Calculate Them)
- Carbohydrates Practice
- Amino Acid Quizzes
25 Fun and Miscellaneous
- Organic Chemistry GIFS - Resonance Forms
- Organic Chemistry and the New MCAT
- A Gallery of Some Interesting Molecules From Nature
- The Organic Chemistry Behind "The Pill"
- Maybe they should call them, "Formal Wins" ?
- Intramolecular Reactions of Alcohols and Ethers
- Planning Organic Synthesis With "Reaction Maps"
- Organic Chemistry Is Shit
- The 8 Types of Arrows In Organic Chemistry, Explained
- The Most Annoying Exceptions in Org 1 (Part 1)
- The Most Annoying Exceptions in Org 1 (Part 2)
- Reproducibility In Organic Chemistry
- Screw Organic Chemistry, I'm Just Going To Write About Cats
- On Cats, Part 1: Conformations and Configurations
- On Cats, Part 2: Cat Line Diagrams
- The Marriage May Be Bad, But the Divorce Still Costs Money
- Why Do Organic Chemists Use Kilocalories?
- What Holds The Nucleus Together?
- 9 Nomenclature Conventions To Know
- How Reactions Are Like Music
Hi James, impressive amount of work in this site. On this page, I think the last two diagrams in the Notes section are out of sequence. The word heat is NOT omitted where the narrative says it is and vice-versa. (Or maybe I misunderstand your point!)
You are correct. Fixed. Thank you so much Len!
This site is just marvellous I never think of it thank u sir
Which pathway do we follow if the reaction in the question takes place at ‘mild heat’; E1 or SN1?
I would assume that “mild heat” is there for a purpose, and it is pushing towards E1.
why is Br considered a strong nucleophile in the second and neutral in the last example???
Thank you
In the second example the “nucleophile” is KOEt which is charged and therefore “strong” (according to our “Quick N’ Dirty” rules). In the fourth example the “nucleophile” is CH3OH which is neutral (and therefore “weak” according to these rules).
The species containing Cl (in the second example) and Br (in the fourth example) are called the “substrate”.
I wish to know what would be the range of those high and low temperatures.
It is vague. But “heat” would generally refer to heating a solution to its boiling point (“reflux”) and the boiling point of most typical solvents for our purposes is 60-100 °C .
its very helpful for me.
After reading it i’m able to decide either the reaction is proceding through sn1/E1 or sn2/E2.
That’s the goal. If it’s helping you, I’m glad.
Dear Dr James
You discussed primary secondary tertiary carbons. What about alilic and benzilic carbons. Will primary benzilic carbon behaves like primary carbon?
Allylic and benzylic carbons will be more prone to going through carbocation pathways (SN1/E1) than typical primary carbons. If a charged nucleophile is present, using the Quick N’ Dirty rules I would generally expect substitution via SN2, and if the nucleophile is neutral (or using the solvent as nucleophile) the SN1 and E1 pathways start to become feasible, particularly with heat.
Well, a good example of this temperature thing is the addition of H2SO4 to primary alcohol. At 413K, elimination takes place to form alkene, but at 443K, ether is formed by SN1. Thank you so much for these thumb rules. Very helpful!
Will sn1 proceed in the reaction of a tertiary halide with ethanol in 25 degrees celsius?
If your question is related to an exam question, the answer is likely “yes”. Applying Quick N’ Dirty rules, tertiary rules out SN2, ethanol (neutral) rules out E2, and room temperature rules out E1. That leaves SN1.
If your question is related to a real-life reaction, my advice would be to go to March’s Advanced Organic Chemistry and look up “solvolysis rates” to get an idea of how quick it will be.
What should be the temperature for breaking C-Br bond ?
That’s not possible to answer without more information.
Fantastic job! Really on the money
I think it should be “In the fourth example we have a tertiary halide” instead of “In the fourth example we have a tertiary alcohol”.
Thank you!
I just wanted to thank you for the awesome website, and method of explanation of concepts you have here. I was struggling with this chapter for days, and reading your instructions, and rules, I understood the concept in an hour! and actually am answering the questions correctly. THANK YOU.
Oh wow, that is great Shahin. Glad to hear it. Keep in mind these ARE Quick N’ Dirty rules and are just a good place to start.
If we have tertiary alkyl halide,water or alcohol and 22 degree celcius what will be reaction?is it E1 or E2?
Likely SN1 – tertiary alkyl halide (not SN2) and weak nucleophile (water or alcohol) [ no E2] in the absence of heat.
Applying Quick N’ Dirty Rules: Tertiary alkyl halide rules out SN2. Water / alcohol rules out E2. Room temperature rules out E1. Why not SN1 ?