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The Cyclohexane Chair Flip – Energy Diagram
Last updated: December 13th, 2022 |
Energy Diagram Of The Cyclohexane Chair Flip
In the last post, we showed a video of a cyclohexane ring flip – turning a cyclohexane chair conformation into a boat and then into the opposite chair.
The key observation we made here was that a chair flip converts all axial groups into equatorial groups and all equatorial groups into axial groups. However all “up” groups remain up and all “down” groups remain down.
Table of Contents
- How Much Does A Cyclohexane Chair Flip “Cost” ? About 10 kcal/mol
- The Cyclohexane Chair Flip Energy Diagram
- The Energy Barrier For A Cyclohexane Chair Flip Is Small Enough To Allow The Two Conformations To Interconvert At Room Temperature
- Summary: The Cyclohexane Chair Flip Energy Diagram
- (Advanced) References and Further Reading
Now that we know what “looks” like to do a chair flip, let’s ask a different question: how much does it “cost”? When we say “cost”, of course, we’re talking about energy. Many organic chemists like to use kcal/mol [to convert to kJ/mol, multiply by 4.184] (See post: Why do Organic Chemists Use Kilocalories)
As you might have noticed while watching the video, converting one cyclohexane into the opposite chair conformation isn’t a matter of doing a simple bond rotation, like it is for, say, “eclipsed” butane into “staggered’ butane. There’s a lot more going on – each C-C bond undergoes rotation of some form.
Let’s walk through it in more detail.
Chair (ground state = 0 kcal/mol) –> Half Chair (+10 kcal/mol above ground state)
First, we take one end of the cyclohexane chair and push it into the “plane” created by the four carbons, making a “half chair”. This first step is actually the most unfavorable – because of a combination of ring and angle strain, the half-chair lies 10 kcal/mol in energy above the chair conformation.
Half-Chair (+10 kcal/mol) –> Twist-Boat (+5.5 kcal/mol)
The next step is to continue pushing that “end” of the half chair up until it is roughly on the same level as the other “end”. This makes a “twist boat”, which is a local energy minimum – we no longer have angle strain (all bonds are again 109°) but there is some torsional strain owing to the fact that there are two pairs of eclipsed C-C bonds. There is also a “flagpole” interaction between the hydrogens on the “prows” but in the twist-boat, they are slightly offset with respect to each other. The twist-boat is 5.5 kcal/mol in energy above the cyclohexane chair.
Twist-Boat (+5.5 kcal/mol) –> Boat (+6.5 kcal/mol) –> Twist Boat (+5.5 kcal/mol)
Where to go from here? Well, the “twist” momentarily passes through a full “boat” conformation (6.5 kcal/mol) on its way to a different “twist”, which is a bit awkward – in the full boat the two “flagpole” hydrogens are held in very close proximity to each other (within each other’s Van Der Waals radius). Think of two friends with long Cyrano de Bergerac noses kissing each other on alternate cheeks – there’s an awkward moment when they briefly bang noses in the middle : – )
Twist-Boat (+5.5 kcal/mol) –> Half Chair (+10 kcal/mol) –> Chair (0 kcal/mol)
From the new twist, we’re merely going backwards to get to the alternate chair – down goes one “prow” to give (momentarily) a half-chair, en route to the flipped chair.
If we draw an energy diagram, the whole process looks like this. Again, note that the chair on the left has the red hydrogens axial, and in the chair on the right, the red hydrogens are now equatorial.
So what? you might ask. We’ve turned one chair into another. Who cares?
[And you might not care. That’s fine. The following discussion is not crucial for us going forward, but is helpful to understand a key consequence of this energy diagram…. ]
3. The Energy Barrier For A Cyclohexane Chair Flip Is Small Enough To Allow The Two Conformations To Interconvert At Room Temperature
For cyclohexane, I cede your point of “who cares”, because for all purposes the two chair forms are identical.
However, things start getting interesting once we start putting any type of substituent on our cyclohexane.
For example, let’s take 1-methylcyclohexane. Let’s say we start with the chair on the left (methyl is axial) and a chair flip converts it into the chair on the right (methyl is equatorial).
First of all, note that these are NOT mirror images of each other – they are different conformations.
Being quite rigid molecules, you would expect “axial” 1-methylcyclohexane to have slightly different properties than “equatorial” 1-methylcyclohexane.
If you could isolate the “axial” conformer, for instance, you’d expect it to have a slightly different melting point and boiling point than the “equatorial” conformer, since the molecules will stack differently with each other.
Furthermore, with other cyclohexanes, the axial and equatorial conformers even have different reactivity (more to come on this in a future chapter).
So how do we handle these differences? Well, we pretty much ignore it. The energy barrier of 10 kcal/mol for this interconversion is large, but not large enough that it prevents these two conformations from interconverting at room temperature (300 Kelvin). In fact these two conformations do interconvert, many times per second.
For our purposes, the bottom line is that you can consider the two chair conformations of 1-methylcyclohexane to be in equilibrium with each other, and furthermore, the properties of the bulk will be a weighted average of the two conformations. [Note 2]
[At low temperatures it’s a different story and the two conformations are “trapped” – we’ll cover that in Note 1 below. ]
In this article the cyclohexane chair flip energy diagram was very simple because the two chair forms are exactly equal in energy. In the next post, we consider the possibility that for substituted cyclohexanes (such as 1-methylcyclohexane) the two chair forms are NOT equal in energy.
First, why might that be? And second, how might that affect the population of the two conformations?
Answers in the next post…
- Substituted Cyclohexanes – Axial vs Equatorial
- Cyclohexane Chair Conformation Stability: Which One Is Lower Energy?
- Ranking The Bulkiness Of Substituents On Cyclohexanes: “A-Values”
- Fused Rings – Cis-Decalin and Trans-Decalin
- Naming Bicyclic Compounds – Fused, Bridged, and Spiro
- Cyclohexane Chair Conformation: An Aerial Tour
- The Cyclohexane Chair Flip
Imagine we have a magical device that can take “snapshots” of molecules, so that we can tell, at any given time, what the structure of a molecule is. Press a button, and presto ! you get pictures of all the molecules in solution.
What would a “snapshot” of a solution of “1-methylcyclohexane” look like? Assume that 1) the molecules will spend >99% of their time in “chair” conformations, and 2) assume (for now) that the two chair forms are equal in energy.
Based on this, we’d expect to see that 50% of the “snapshots” show “axial” 1-methylcyclohexane, and 50% show “equatorial” 1-methylcyclohexane.
[We actually do have a device which does this, and it’s not magic – it’s called an NMR spectrometer – more on that in a later series].
So what do we actually see?
Here’s the cool part.
At very low temperatures (–78°C, which is the temperature of the cheap dry ice/acetone cold bath) our “magic device” does indeed show that there is a mixture of equatorial and axial 1-methylcyclohexane in solution, just like we might expect.
However, when we let it warm up to room temperature, something interesting happens. The “snapshots” of the “axial” and “equatorial” 1-methylcyclohexane start blurring together, until we see a single signal that is an average of those two snapshots.
So what could explain this? Why might we see two “snapshots” at low temperature, but a single, “blended” snapshot at high temperature?
Does it remind you of something? Maybe of the difference between taking pictures of a ceiling fan at rest (where you can see the individual blades) and taking pictures at high speed (where you just see a blur). Or spokes on a bicycle? Or a colour wheel?
We see a “blur” on our magic snapshot machine (i.e. an NMR spectrometer) because, like a camera with a long shutter speed, we see an average of the different states over time.
A similar type of thing is happening here. At low temperatures, we have separate populations of “axial” and “equatorial” 1-methylcyclohexane, which do not have sufficent energy to ascend the 10 kcal/mol barrier (through the “half-chair”) that would allow for their interconversion.
At higher temperature, there is sufficient energy for each molecule to ascend the barrier to half-chair formation, and therefore the interconversion can occur.
Note 2 – Chiral conformations . Soon enough you will cover chirality. With some substituted cyclohexanes (e.g. cis-1,2-dimethylcyclohexane) you may note that each chair conformation is chiral, and the two chair conformations are enantiomers of each other. However, the molecule is considered to be “achiral” overall since the two chiral enantiomers are in equilibrium with each other and the optical activity of these two conformations cancels out. That’s what I meant by “the properties of the molecule as a whole will be the weighted average of the conformations. ”
This is a topic commonly taught to undergraduates in Organic Chemistry. Cyclohexane’s ground state conformation is the chair, and it can undergo a ring ‘flip’, where axial substituents become equatorial substituents. This flip goes through some higher-energy intermediates (the boat, half-boat, and twist-chair).
- Ueber die geometrischen Isomerien der Hexamethylenderivate
Chem. Ber. 1890, 23 (1), 1363-1370
The conformations of cyclohexane and related six-membered rings have been of active interest since at least 1890.
- Die Baeyersche Spannungstheorie und die Struktur des Diamanten
Journal für Praktische Chemie 1918, 98 (1), 315-353
A very early paper on the 3-D model of cyclohexane, showing that it is not flat, and providing models for the chair conformation.
- The conformation of the steroid nucleus
H. R. Barton
Experientia 1950, 6, 316-320
This early paper by Nobel Laureate Sir Prof. D. H. R. Barton is on the conformational analysis of cyclohexanes and later applies this to the 3-D structure of steroids (which contain several fused 6-membered rings). He notes that cyclohexane confomers can interconvert, stating, “a small difference in free energy content (about one kilocal, at room temperature) between two possible conformations will ensure that the molecule appears by physical methods of examination and by thermodynamic considerations to be substantially in only one conformation.”
- Nomenclature of cycloHexane Bonds
BARTON, D., HASSEL, O., PITZER, K., PRELOG, V.
Nature 1953, 172, 1096–1097
- Nomenclature of Cyclohexane Bonds
H. R. Barton, O. Hassel, K. S. Pitzer, V. Prelog
Science 1954, 119, 49
These are the first instances of the terms ‘axial’ and ‘equatorial’ being used to denote the two positions substituents can take in cyclohexane. This was also back in the day when scientists could safely cross-publish to get better visibility – pretty much the same article is published in both Science and Nature, considered top journals.
- Nuclear Magnetic Resonance Line-Shape and Double-Resonance Studies of Ring Inversion in Cyclohexane-d11
A. L. Anet and A. J. R. Bourn
Journal of the American Chemical Society 1967, 89 (4), 760-768
This paper covers a classic experiment and is commonly mentioned in undergraduate and graduate organic chemistry or NMR courses. At room temperature, cyclohexane gives one signal because interconversion of chair forms occurs rapidly. At low temperatures, however, it gives a very complex 1H NMR spectrum. At low temperatures interconversions are slow; the chemical shifts of the axial and equatorial protons are resolved, and complex spin-spin couplings occur. At -100 °C, however, cyclohexane-d11 gives only 2 signals of equal intensity. These signals correspond to the axial and equatorial hydrogen atoms. Interconversions between these conformations occur slowly at this low temperature, but they happen slowly enough for the NMR spectrometer to detect the individual conformations (the nucleus of a deuteron has a much smaller magnetic moment than a proton, and signals from deuteron absorption do not occur in 1H NMR spectra). Prof. F. A. L. Anet is an Emeritus Professor at UCLA and was a pioneer in the use of NMR spectroscopy for conformational analysis.
- Non‐Chair Conformations of Six‐Membered Rings
M. Kellie, F. G. Riddell
Topics in Stereochemistry 1974, 8
This reference contains useful information on the inversion barrier for cyclohexane, as well being the first paper to actually invoke the ‘twist-boat’ conformation during this process.
- Conformational equilibrium trapping by high-vacuum cryogenic deposition
A. L. Anet and M. Squillacote
Journal of the American Chemical Society 1975, 97 (11), 3243-3244
The chair-twist energy difference has been directly measured by low-termperature IR spectroscopy. The chair was determined to be 5.5 kcal/mol lower in enthalpy than the twist.
- Conformational structure, energy, and inversion rates of cyclohexane and some related oxanes
Herbert L. Strauss and Herbert M. Pickett
Journal of the American Chemical Society 1970, 92 (25), 7281-7290
This paper describes a theoretical method for setting up calculations for ring inversion.
- Conformational analysis. 130. MM2. A hydrocarbon force field utilizing V1 and V2 torsional terms
Norman L. Allinger
Journal of the American Chemical Society 1977, 99 (25), 8127-8134
The MM2 (Molecular Mechanics 2) method was developed by Prof. Allinger for conformational analysis of hydrocarbons and other small organic molecules. This paper documents results for calculations using this method, including the ring inversion of cyclohexane. MM methods are considered crude nowadays because they neglect quantum and relativistic effects, but they are nonetheless useful for doing initial geometry optimization of a structure before doing a higher-level calculation.
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
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
- 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
- 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
- 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
- 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
- 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
- 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
- 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