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Newman Projection of Butane (and Gauche Conformation)
Last updated: November 6th, 2023 |
The Conformational Isomers (and Newman Projections) of Butane
In two previous articles we’ve discussed the conformations of ethane and propane and saw that their staggered conformations were lower in energy than their eclipsed conformations. The barrier to rotation in each (the “torsional strain” of the higher-energy, eclipsed conformation versus the lower-energy eclipsed conformation) was 3.0 kcal/mol in ethane and 3.4 kcal/mol in propane.
So what about the next hydrocarbon up: butane?
In contrast to ethane and propane, which have a single rotational barrier, the situation for butane is a bit more complicated (or as we sometimes say, “more fun”). The highest energy conformation in butane is about 5 kcal/mol above the lowest-energy conformation. But that’s not the only energy maximum; when rotated about the C2-C3 axis.
The video below summarizes the full rotational energy profile looks like when we look along the C2-C3 bond and rotate in 60 degree increments.
We can even graph the energy of the different conformations in 60 degree increments.
Wait – where did this come from? And what is this “gauche conformation” thing?
Fear not! We’re going to go through how we got here in detail, starting with the absolute basics.
Table of Contents
- Staggered And Eclipsed Conformations Of Butane
- Focus On The Central C2-C3 Bond Of Butane
- Newman Projections Of Butane: Staggered and Eclipsed
- “Steric Interactions” In The syn- Conformation of Butane
- The CH3-CH3 Eclipsing Interaction In Butane “Costs” About 3 kcal/mol
- Two More Eclipsed Conformations Of Butane
- The Gauche Conformation of Butane – Not All Staggered Conformations Are Equal!
- Graphing Out The Conformations of Butane
- Newman Projections of Butane: Conclusion
- Appendix: What About C1-C2?
- Notes
- Quiz Yourself!
- (Advanced) References and Further Reading
1. Staggered And Eclipsed Conformations Of Butane
Let’s get started by drawing butane in the laziest way possible, with all carbons in the plane of the page; the line diagram drawn with the carbons zig-zagging nicely.
With a bit more effort, we can also expand out the C-H bonds; if we choose to draw all the C-C bonds as staggered, we get the molecule drawn above-right.
Since all the bonds in butane are sigma bonds, and therefore may rotate freely, a perfectly acceptable alternate way to draw butane would be like this, which represents a different conformation of butane where the C2-C3 bond has been notably rotated:
Here, we’ve chosen to draw out the C-H bonds with all the C-C bonds eclipsed.
Since there is free rotation about all the single bonds, these conformations can interconvert.
Model kit time. Here is a gif showing rotation about the C2-C3 bond, interconverting the C2-C3 “staggered” conformation to a C2-C3 “eclipsed” conformation.
So far, so good
[Note 1 – yes, pulled a bit of a fast one there]
2. Focus On The Central C2-C3 Bond Of Butane
Butane has 3 carbon-carbon bonds that can each rotate freely. At first glance, that might seem intimidating to analyze. However, we’re only going to analyze rotation about the central (C2-C3) bond here.
Here’s why.
Say you were at a dinner party, and someone asked you to analyze the whole conformation of butane. Your mind races. “Does the orientation about C1-C2 affect the energy about C2-C3?”.
As it turns out, these three terms are independent and can for our purposes, can be analyzed in isolation. That means that rotations about C1-C2 and C3-C4 don’t affect the torsional strain about C2-C3.
So you’d pull out your pen and calmly do the following analysis:
total torsional strain of butane = [torsional strain of C1-C2 bond] + [torsional strain of C2-C3 bond] + [torsional strain of C3-C4 bond].
This makes our lives much easier, which is why reductionism is awesome.
Also, it turns out that the torsional strain about C1-C2 and C3-C4 in butane is very similar to propane, which we analyzed in the last post.
Bottom line: we’re going to ignore the conformations about C1-C2 and C3-C4 and just focus on the interactions we haven’t seen before.
BTW If you really are aching to see the C1-C2 conformation of butane, it’s in the notes [1]
It will really simplify things from now on if we just draw butane like this:
3. Newman Projections Of Butane: Staggered And Eclipsed
Now it’s time for some Newman projections.
Here, we’re going to take our model of butane in the staggered conformation and look along the C2-C3 bond. When we do that we can sketch out the Newman projection like this:
Note that the two methyl groups point up and down like the hour and minute hands on Big Ben when it strikes 6:00 . The dihedral angle between these two methyl groups is 180°; we say that their relative orientation is anti (anti-periplanar to be more specific).
Likewise, if we look along C2-C3 of the eclipsed conformation of butane, we get this:
In this case the two methyl groups have a dihedral angle of 0°, and we say that their relative orientation is syn. [Note 2] [Quick reminder: eclipsed and staggered refer to the orientation of all the substituents on the front with respect to the substituents on the back, while syn and anti refers to relative orientation between two specific groups, although we will muddy the waters sometimes and refer to CH3 – CH3 “eclipsing” interactions and H-H “eclipsing” interactions.]
4. “Steric Interactions” In Butane
Let’s have a closer look at these two conformations. According to these measurements and calculations [Ref 1] the torsional strain of the C2-C3 syn conformation is about 5.0 kcal/mol higher than the C2-C3 anti conformation.
Why so high?
The issue here is that when electron clouds surrounding the hydrogens on the CH3 groups are brought too close together, there are electron-electron repulsions (like charges repel, after all), and this is destabilizing; their natural inclination is to “push away” from each other, much like two magnets of the same polarity push apart when brought close together.
[It’s not unlike repulsions between bonding pairs that give rise to the different molecular geometries of atoms we see in VSEPR theory (trigonal planar, tetrahedral, etc.) , except that these repulsions occur between electrons that are farther away. ]
This interaction in butane is often called the CH3 – CH3 “eclipsing” interaction. It’s an example of what we often call a “steric interaction” or often, colloquially, just “sterics”.
5. The CH3-CH3 Eclipsing Interaction In Butane “Costs” About 3 kcal/mol
If we know that the torsional strain of the CH3-CH3 syn conformation of butane is about 5 kcal/mol relative to CH3-CH3 anti we can figure out how much the CH3-CH3 interaction “costs”.
How so?
We’ve seen previously that each H-H eclipsing interaction costs about 1 kcal/mol. So if we subtract out the two H-H eclipsing interactions, that leaves us with about 3 kcal/mol for the CH3-CH3 interaction.
If we add the CH3-CH3 eclipsing interaction to our “price list” for steric interactions, we get this.
6. Two More Eclipsed Conformations Of Butane
Now we can start to look at some other conformations of butane. Let’s look at the two other eclipsed conformations, ones where the dihedral angle between the methyl groups is at 120° and 240° respectively.
Using the “price list” above, it’s possible to come up with a very good estimate for the torsional strain in this conformation.
We just need to break down all the eclipsing interactions and check their values on the “price list”.
If we add up the two eclipsing CH3-H interactions (1.4 kcal/mol) and the H-H eclipsing interaction (1.0 kcal/mol) we get 3.8 kcal/mol. This is very close to the experimental value of 3.6 kcal/mol.
Reductionism works pretty well!
7. Not All Staggered Conformations Are Equal – The Gauche Conformation of Butane
We’re almost done. Let’s look at the two other “staggered” conformations of butane, those with a dihedral angle between methyl groups of 60° and 300° respectively.
Since the substituents on C2 are staggered with respect to the three groups on C3, you might initially think the strain in these conformations is zero. That’s not quite true.
The two conformations have a torsional strain of about +0.9 kcal/mol relative to the anti conformation.
Why? As it turns out these methyl groups are not so far apart. The calculated distance between the two methyl groups is about 3.1 Å, which is not far from the distance of 2.9 Å in the syn orientation, meaning they are still quite close together.
This minor steric interaction has come to be known as the “gauche” conformation – gauche meaning, “awkward”.
The gauche interaction comes up in the chair form of cyclohexane. [Note 3]. A methyl group in the axial position will experience two gauche interactions with the neighboring C-C bonds, resulting in the 1.8 kcal/mol energy difference (or “A-value”) observed for axial vs equatorial methyl groups in cyclohexanes. [See post: Ranking The Bulkiness Of Substituents On Cyclohexanes – “A Values”]
8. Graphing Out The Conformations Of Butane
Now that we’ve explored the conformational isomers of butane (in 60° increments) let’s summarize by showing a Newman projection of butane along the C2-C3 bond with the methyl groups syn and sweep the back methyl group through a rotation of 360°.
We can even graph out each of the conformations of butane and put in a diagram like this. From this graph we can see that butane has three barriers to rotation along the C2-C3 bond.
9. Newman Projections of Butane: Conclusion
So what did we learn? Here are some key points.
- Steric interactions are what we call repulsions between the electron clouds of substituents that come into close contact, such as in the eclipsed conformation of butane where the two methyl groups are syn. In order to reduce steric interactions, bonds and bond angles deform ever-so-slightly from their ideal values, resulting in strain.
- Strain results in small barriers to rotation between conformations, which can be measured experimentally and calculated using advanced computational methods we won’t get into [e.g. Ref 1]
- In contrast to ethane, propane, and the C1-C2 bond of butane, along the C2-C3 bond of butane not all energy maxima (the peaks on the graph above) have the same energy. The energy maxima correspond to the eclipsed conformation with both methyl groups syn (dihedral angle 0°, strain energy about 5 kcal/mol) and the two remaining eclipsed conformations (dihedral angles 120° and 240°, strain energy about 3.6 kcal/mol).
- The C2-C3 bond of butane has two new steric interactions we did not see in ethane or propane. The first is the CH3-CH3 eclipsing interaction, which introduces about 3.0 kcal/mol of strain.
- The gauche interaction occurs in butane occurs when the two methyl groups have dihedral angles of 60° and 300° and arises because the methyl groups are still quite close together (about 3.1 Å, compare to 2.9 Å) for the syn– conformation. The strain energy of the gauche interaction is about 0.9 kcal/mol. (We’ll see this again when we discuss conformations of cyclohexanes.)
- Given a list of the “costs” of various steric interactions, we can make good estimates for the strain energies of various conformations. For the two eclipsed conformations with dihedral angles of 120° and 240° we saw that we could make a pretty good guess of its strain energy using previously determined values of 1 kcal/mol and 1.4 kcal/mol for the H-H and CH3-H eclipsing interactions, respectively . Don’t be surprised to see questions like this on exams! :-)
Appendix – What About The C1 C2 Rotation of Butane?
The C1-C2 bond in butane has a single barrier to rotation, just like propane. The ethyl group isn’t actually that much “bigger” than the methyl group for our purposes, because the CH3 at the end of the methyl group can just point away from C-C, resulting in very little additional strain:
(If you’re familiar with A-values, the A-value of ethyl (1.75 kcal/mol) is only slightly larger than that for methyl (1.7 kcal/mol).
Notes
Related Articles
- Ranking The Bulkiness Of Substituents On Cyclohexanes: “A-Values”
- Assigning R/S To Newman Projections (And Converting Newman To Line Diagrams)
- Introduction to Cycloalkanes (1)
- Staggered vs Eclipsed Conformations of Ethane
- Conformational Isomers of Propane
- Newman Projection Practice
- On Cats, Part 3: Newman Projections
- Substituted Cyclohexanes – Axial vs Equatorial
- How To Draw A Bond Rotation
Many thanks to Jeremy Tran for drawing out the rotational energy profile of butane.
The cat diagram was done by the brilliant Canadian political cartoonist Graeme Mackay who is more used to drawing heads of state.
Note 1. The methyl groups on C1 and C4 were collapsed here as CH3 since otherwise we’d have to show rotation about C1-C2 and C3-C4 to get the “all staggered” conformation to transform to the “all eclipsed” conformation, and that would be annoying.
Note 2. If the dihedral angle between two substituents is acute (ranges from -90° < 0 < +90°) they are said to be “syn”. If the dihedral angle is obtuse +90°< 180 <270° (-90°) they are “anti”.
Between the dihedral angles of +30° and -30° and 150° and -150° (210°) two substituents are said to be “periplanar”, i.e. in the same plane (or roughly so). Substituents that are not periplanar are said to be “clinal” (+30° to 150° and -30° to -150°).
So there are four possibilities; syn-periplanar, anti-periplanar, syn-clinal (+ and -) and anti-clinal (+ and -). We generally don’t discuss clinal in introductory organic chemistry (since it interferes with our discussion of gauche) but hey, now you know. The terminology comes from Klyne and Prelog (Ref 6)
Note 3. If you compare the axial and equatorial conformations of 1-methylcyclohexane, the axial conformation has two gauche interactions that the equatorial methyl group does not have. These roughly total 1.7 kcal/mol.
Quiz Yourself!
(Advanced) References and Further Reading
The value for the rotational barrier of butane has measured by several experimental techniques, as well as calculated by theoretical methods. These methods do not always agree. Eliel’s Stereochemistry of Organic Compounds has a much deeper discussion of these issues than you will find in any other textbook or online resource. Textbooks (and Wikipedia, which cites 19 kJ/mol (4.5 kcal/mol in a diagram and 5.0 kcal/mol in the text) differ in their published values for the rotational barrier for butane.
- The syn rotational barrier in butane
Norman L. Allinger, Roger S. Grev, Brian F. Yates, and Henry F. Schaefer III
Journal of the American Chemical Society 1990, 112 (1), 114-118
DOI: 1021/ja00157a018
This is the source of the values used for the conformational barriers in butane in this article (0.9 kcal/mol for gauche and 5.1 kcal/mol for butane) calculated by molecular mechanics methods. - Far infrared spectrum and conformational potential function of n-butane
Howard D. Stidham, J.R. Durig
Spectrochimica Acta Part A: Molecular Spectroscopy, 1986 Volume 42, Issues 2–3, 105-111
DOI: 10.1016/0584-8539(86)80169-6
Measurement of the rotational barrier in butane by far-IR spectroscopy. “The s–trans to gauche, gauche to gauche, and gauche to s–trans barriers in cm−1 were found to be: 1315 (3.76 kcal/mol), 1090 (3.12 kcal/mol) and 1070 (3.06 kcal/mol), respectively” - Rotational barriers. 2. Energies of alkane rotamers. An examination of gauche interactions
Kenneth B. Wiberg and Mark A. Murcko
Journal of the American Chemical Society 1988, 110 (24), 8029-8038
DOI: 1021/ja00232a012
Calculation of the rotational barrier in butane by ab initio methods; gives a barrier of >6 kcal/mol. - Carbon−Carbon Rotational Barriers in Butane, 1-Butene, and 1,3-Butadiene
Mark A. Murcko, Henry Castejon, and Kenneth B. Wiberg
The Journal of Physical Chemistry 1996, 100 (40), 16162-16168
DOI: 1021/jp9621742
“The difference in energy between the syn and anti forms of butane at 298 K is 5.1 kcal/mol, which is significantly larger than the experimental estimate. However, it is shown that a reliable experimental estimate of the barrier cannot be made based on the currently available data.” - A Critical Analysis on the Rotation Barriers in Butane
Yirong Mo
The Journal of Organic Chemistry 2010, 75 (8), 2733-2736
DOI: 1021/jo1001164
Study on hyperconjugation in the rotational barrier for butane. “[Our] results show that although there are stronger hyperconjugative interactions in the staggered anti and gauche conformers than the eclipsed structures, the energy curve and barriers are dominated by the steric repulsion.” - Description of steric relationships across single bonds.
Klyne, W., Prelog, V.
Experientia 16, 521–523 (1960).
DOI: 10.1007/BF02158433
The Klyne-Prelog notation for stating the conformational isomers of butane.In contrast to ethane and propane, which have a single barrier to rotation, butane has three barriers to rotation, of varying heights, when rotated about the C2-C3 axis.
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
- 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"
- 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
- Learning New Reactions: How Do The Electrons Move?
- 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
- 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
- Learning Organic Chemistry Reactions: A Checklist (PDF)
- 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
- Stereochemistry Practice Problems and Quizzes
08 Substitution Reactions
- Nucleophilic Substitution Reactions - 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
- 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
- SN1 vs E1 and SN2 vs E2 : The Temperature
- Deciding SN1/SN2/E1/E2 - The Solvent
- Wrapup: The Key Factors For Determining 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
- Alkene Addition Reactions: "Regioselectivity" and "Stereoselectivity" (Syn/Anti)
- Stereoselective and Stereospecific Reactions
- Hydrohalogenation of Alkenes and Markovnikov's Rule
- Hydration of Alkenes With Aqueous Acid
- Rearrangements in Alkene Addition Reactions
- Halogenation of Alkenes and Halohydrin Formation
- Oxymercuration Demercuration of Alkenes
- Hydroboration Oxidation of Alkenes
- m-CPBA (meta-chloroperoxybenzoic acid)
- OsO4 (Osmium Tetroxide) for Dihydroxylation of Alkenes
- Palladium on Carbon (Pd/C) for Catalytic Hydrogenation of Alkenes
- Cyclopropanation of Alkenes
- 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
- Partial Reduction of Alkynes With Na/NH3 To Obtain Trans Alkenes
- Alkyne Hydroboration With "R2BH"
- Hydration and Oxymercuration of Alkynes
- Hydrohalogenation of Alkynes
- 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
- A Gallery of Some Interesting Molecules From Nature
- 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
- On Cats, Part 4: Enantiocats
- On Cats, Part 6: Stereocenters
- Organic Chemistry Is Shit
- The Organic Chemistry Behind "The Pill"
- Maybe they should call them, "Formal Wins" ?
- Why Do Organic Chemists Use Kilocalories?
- The Principle of Least Effort
- Organic Chemistry GIFS - Resonance Forms
- Reproducibility In Organic Chemistry
- What Holds The Nucleus Together?
- How Reactions Are Like Music
- Organic Chemistry and the New MCAT
26 Organic Chemistry Tips and Tricks
- Common Mistakes: Formal Charges Can Mislead
- Partial Charges Give Clues About Electron Flow
- Draw The Ugly Version First
- Organic Chemistry Study Tips: Learn the Trends
- The 8 Types of Arrows In Organic Chemistry, Explained
- Top 10 Skills To Master Before An Organic Chemistry 2 Final
- Common Mistakes with Carbonyls: Carboxylic Acids... Are Acids!
- Planning Organic Synthesis With "Reaction Maps"
- Alkene Addition Pattern #1: The "Carbocation Pathway"
- Alkene Addition Pattern #2: The "Three-Membered Ring" Pathway
- Alkene Addition Pattern #3: The "Concerted" Pathway
- Number Your Carbons!
- The 4 Major Classes of Reactions in Org 1
- How (and why) electrons flow
- Grossman's Rule
- Three Exam Tips
- A 3-Step Method For Thinking Through Synthesis Problems
- Putting It Together
- Putting Diels-Alder Products in Perspective
- The Ups and Downs of Cyclohexanes
- The Most Annoying Exceptions in Org 1 (Part 1)
- The Most Annoying Exceptions in Org 1 (Part 2)
- The Marriage May Be Bad, But the Divorce Still Costs Money
- 9 Nomenclature Conventions To Know
- Nucleophile attacks Electrophile
27 Case Studies of Successful O-Chem Students
- Success Stories: How Corina Got The The "Hard" Professor - And Got An A+ Anyway
- How Helena Aced Organic Chemistry
- From a "Drop" To B+ in Org 2 – How A Hard Working Student Turned It Around
- How Serge Aced Organic Chemistry
- Success Stories: How Zach Aced Organic Chemistry 1
- Success Stories: How Kari Went From C– to B+
- How Esther Bounced Back From a "C" To Get A's In Organic Chemistry 1 And 2
- How Tyrell Got The Highest Grade In Her Organic Chemistry Course
- This Is Why Students Use Flashcards
- Success Stories: How Stu Aced Organic Chemistry
- How John Pulled Up His Organic Chemistry Exam Grades
- Success Stories: How Nathan Aced Organic Chemistry (Without It Taking Over His Life)
- How Chris Aced Org 1 and Org 2
- Interview: How Jay Got an A+ In Organic Chemistry
- How to Do Well in Organic Chemistry: One Student's Advice
- "America's Top TA" Shares His Secrets For Teaching O-Chem
- "Organic Chemistry Is Like..." - A Few Metaphors
- How To Do Well In Organic Chemistry: Advice From A Tutor
- Guest post: "I went from being afraid of tests to actually looking forward to them".
In the cat drawing by MackayCartoons, shouldn’t the antiperiplaner be 0 kcal/mol and the syn periplaner be 5kcal/mol? I believe they were accidently switched.
Yes, thank you for spotting. They were accidentally switched and this has now been fixed.
Awesome, I am following last couple of months, helpful and improved myself.
Glad you find the site useful.