Stereochemistry and Chirality
By James Ashenhurst
What’s a Racemic Mixture?
Last updated: March 22nd, 2019
What do you notice about these three pictures? Count the number of left gloves and right gloves.
6 left and 6 right gloves, correct?
What about this one:
I count 8 right gloves, 4 left gloves. So there’s a slight excess of right gloves here.
Finally, this figure:
ONLY right hand gloves here. 12 right gloves, zero left gloves.
So what does this have to do with organic chemistry?
Gloves are chiral objects. That is, they lack an internal plane of symmetry. Left gloves and right gloves are mirror images of each other, but they can’t be superimposed.
In chemistry, there’s a word we have to describe a pair of non-superimposable mirror images – they’re called enantiomers.
Tying it back to the drawings, we can have three types of situations.
- In the first drawing, we have an equal number of left and right gloves (i.e. enantiomers). This is called a racemic mixture of enantiomers.
- In the second drawing, we have an excess of right gloves compared to left gloves. In a situtation like this we can say we have an “enantiomeric excess” of gloves, or alternatively, the mixture is “enantioenriched” in the right-hand glove. [We can also calculate the “excess” here: the mixture is 66% right and 33% left – so we have a 33% “excess” of the right-hand enantiomer].
- In the third drawing, we have only right-hand gloves. This is said to be an “enantiomerically pure” mixture of gloves, since we have only one enantiomer present.

- A solution containing equal amounts of (R)-2-butanol and (S)-2-butanol is a racemic mixture.
- A solution containing an excess of either the (R)-enantiomer or the (S)-enantiomer would be enantioenriched.
- A solution containing only the (R)-enantiomer or the (S)-enantiomer will be enantiomerically pure.

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- From Gen Chem to Organic Chem, Pt. 2 - Electrons and Orbitals
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- From Gen Chem to Organic Chem, Part 14: Wrapup
01 Bonding, Structure, and Resonance
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- Review of Atomic Orbitals for Organic Chemistry
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- Hybrid Orbitals
- A Hybridization Shortcut
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02 Acid Base Reactions
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- Acid Base Reactions Are Fast
- Putting Acidity In Perspective
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03 Alkanes and Nomenclature
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- Meet the (Most Important) Functional Groups
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04 Conformations and Cycloalkanes
- Conformations
- Newman Projections
- Putting the Newman into ACTION
- Introduction to Cycloalkanes (1)
- Cis And Trans Cycloalkanes
- Cycloalkanes - How To Calculate Ring Strain
- Cycloalkanes - Ring Strain In Cyclopropane And Cyclobutane
- Ring Strain in Cyclopentane and Cyclohexane
- An Aerial Tour Of The Cyclohexane Chair
- How To Draw A Cyclohexane Chair
- The Cyclohexane Chair Flip
- The Cyclohexane Chair Flip - Energy Diagram
- Substituted Cyclohexanes - Equatorial vs Axial
- Substituted Cyclohexanes: "A Values"
- The Ups and Downs of Cyclohexanes
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- Fused Rings
- Bridged Bicyclic Rings (And How To Name Them)
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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)
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- Free Radical Reactions
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- Free Radical Initiation: Why Is "Light" Or "Heat" Required?
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07 Stereochemistry and Chirality
- On Cats, Part 4: Enantiocats
- On Cats, Part 6: Stereocenters
- The Single Swap Rule
- Introduction to Assigning (R) and (S): The Cahn-Ingold-Prelog Rules
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- The Meso Trap
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- The SN2 Mechanism
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- 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
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09 Elimination Reactions
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- Elimination Reactions (2): Zaitsev's Rule
- Elimination Reactions Are Favored By Heat
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- The E1 Reaction
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11 SN1/SN2/E1/E2 Decision
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- Intramolecular Reactions of Alcohols and Ethers
- Protecting Groups For Alcohols
- Thiols And Thioethers
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15 Organometallics
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- Reactions of Grignard Reagents
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- Grignard Reactions And Synthesis (2)
- Gilman Reagents (Organocuprates): How They're Made
- Gilman Reagents (Organocuprates): What They're Used For
- Common Mistakes with Carbonyls: Carboxylic Acids... Are Acids!
- The Heck, Suzuki, and Olefin Metathesis Reactions (And Why They Don't Belong In Most Introductory Organic Chemistry Courses)
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16 Spectroscopy
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- How Bleach Works: Understanding Colors From Nature
- Introduction To UV-Vis Spectroscopy
- UV-Vis Spectroscopy: Absorbance of Carbonyls
- UV-Vis Spectroscopy: Some Practice Questions
- Bond Vibrations, IR Spectroscopy, and the "Ball and Spring" Model
- Infrared Spectroscopy: A Quick Primer On Interpreting Spectra
- IR Spectroscopy: Some Simple Practice Problems
- Homotopic, Enantiotopic, Diastereotopic
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- Structure Determination Case Study: Deer Tarsal Gland Pheromone
17 Dienes and MO Theory
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- Conjugation and Resonance
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- Pi Molecular Orbitals of Butadiene
- Reactions of Dienes: 1,2 and 1,4 Addition
- Thermodynamic and Kinetic Control
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- 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
- Molecular Orbitals 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
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18 Aromaticity
19 Reactions of Aromatic Molecules
- Electrophilic Aromatic Substitution: Introduction
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- Electrophilic Aromatic Substitution - The Mechanism
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- Understanding Ortho, Para, and Meta Directors
- Why are halogens ortho- para- directors?
- Disubstituted Benzenes: The Strongest Electron-Donor "Wins"
- Electrophilic Aromatic Substitutions (1) - Halogenation
- 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 of Diazonium Salts: Sandmeyer and Related Reactions
- 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"
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20 Aldehydes and Ketones
- Weird Nomenclature In Carbonyl Chemistry
- The Simple Two-Step Pattern For Seven Key Reactions of Aldehydes and Ketones
- Wittig Reaction
- Imines and Enamines
- Acid Catalysis Of Carbonyl Addition Reactions: Too Much Of A Good Thing?
- On Acetals and Hemiacetals
- Carbonyl Chemistry: 10 Key Concepts (Part 1)
- Carbonyls: 10 key concepts (Part 2)
- Breaking Down Carbonyl Reaction Mechanisms: Anionic Nucleophiles (Part 1)
- Breaking Down Carbonyl Reaction Mechanisms: Reactions of Anionic Nucleophiles (Part 2)
21 Carboxylic Acid Derivatives
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- Carbonyl Mechanisms: Neutral Nucleophiles, Part 1
- Carbonyl chemistry: Anionic versus Neutral Nucleophiles
- Proton Transfers Can Be Tricky
- Let's Talk About the [1,2] Elimination
- Carbonyl Chemistry: Learn Six Mechanisms For the Price Of One
- Summary Sheet #5 - 9 Key Mechanisms in Carbonyl Chemistry
- Summary Sheet #7 - 21 Carbonyl Mechanisms on 1 page
- How Reactions Are Like Music
- Making Music With Mechanisms
- The Magic Wand of Proton Transfer
- The Power of Acid Catalysis
22 Enols and Enolates
23 Amines
- Amides: Properties, Synthesis, and Nomenclature
- Basicity of Amines And pKaH
- 5 Factors That Affect Basicity 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
- Introduction to Peptide Synthesis
- The Strecker Synthesis of Amino Acids
24 Carbohydrates
- D and L Sugars
- What is Mutarotation?
- Reducing Sugars
- Pyranoses and Furanoses: Ring-Chain Tautomerism In Sugars
- The Big Damn Post Of Sugar Nomenclature
- 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
25 Fun and Miscellaneous
- 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" ?
- Introduction To Synthesis
- 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)
- Org 1 Review Quizzes
- 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
This is exactly what i was thought by proff Anam. All thanks ti this website it has enlighten me the more. All thanks to all who had successfully made this page
Thank you so much this makes so much sense!!!
Really creative way of explaining…hatsoff
thank you soooooo much >> its is very creative way fo explaining :)
Come be my chemistry teacher please ! love the use of the gloves ! thank you so much
Can we predict when we will get a racemic mixture?
This is the best explanation I’ve ever read on this topic! Awesome!
I love you and your website. Saved so much headache!!
Thanks for that! Somehow seeing it that way makes so much more sense!
Can we always assume that ketones are always achiral & aldehydes are chiral?
Thank you for breaking it down with the use of gloves, great technique, I definitely understand what a Racemic mixture is now.
Thank. The explanation is crystal clear
Those gloves look so creepy it gave me a panic attack
Can someone please answer this question for me? if the starting compound is racemic, will the product also be racemic?)
Yes, with two caveats: 1) your reagent is achiral, and 2) the reaction does not lead to destruction of any stereoisomers. As a counter-example of the latter, oxidation of racemic 2-butanol will give 2-butanone, which is an achiral molecule (not racemic)
Thank you so much
I have one last question.
Isopulegone is isolated from the reaction and then treated with sodium hydroxide in ethanol.Under the equilibrium conditions of this base-catalyzed isomerization, pulegone is the favored product and, after workup, is isolated as a crude oil (why is pulegone, rather than isopulegone, strongly favored in this equilibrium?
I have one last question.
Isopulegone is isolated from the reaction and then treated with sodium hydroxide in ethanol.Under the equilibrium conditions of this base-catalyzed isomerization, pulegone is the favored product and, after workup, is isolated as a crude oil (why is pulegone, rather than isopulegone, strongly favored in this equilibrium?
What does it matter if you have racemic mixture of something or not? Does it only matter to a chemist? Because when Primatene Mist disappeared from the world, the only OTC asthma medicine now clearly states “racemic epinephrine” Why? Who cares? Why mention it on the label? Is there a functional difference in drug manufacturing? After all we don’t say “isomer of…” for everything that is a drug and an isomer (the diff between generics is often isomers and it affects people especially in psychiatry, though it’s assumed that it does’t matter). So, why say “racemic” on the asthma med then?
Hi Selma
Great question. Quick answer is: making the racemic version is cheaper and it is almost as effective.
Longer answer below
Epinephrine has a chiral center and thus could exist as one or another optical isomer, or “enantiomer”. When it comes to drugs, enantiomers often have very different medicinal properties. The classic example is thalidomide [where one enantiomer cured morning sickness and the other caused birth defects] , but this is true even of common drugs on the market today such as the antidepressant Celexa (citalopram) where one enantiomer is more active than the other.
The differing effectiveness of enantiomers exists because your enzymes and proteins, for example, also exist as single enantiomers and just like a left hand fits well in a left-handed glove but not a right-hand one, each enantiomer will have a different “fit” within the active site of the protein, causing different effects.
Like any other product, manufacturers of drugs have to be mindful of costs, especially in the case of a non patent-protected medicine like epinephrine.
While it is certainly possible to make epinephrine in either the pure “D” or “L” forms, it adds extra costs to the process. Making it as the “racemic” version (DL) is generally cheaper. For most purposes it is just as effective.
In the case of epinephrine, Wikipedia tells me that the L form is the active component and the D form is inactive. So long as the D form is merely inactive and not actually harmful, it’s cheaper to just make the racemic version and just use double the dose of what you would use for the pure L form.
The only thing to worry about is cases where the other enantiomer is actually toxic. Thalidomide is the classic example. In the case of epinephrine it is not a problem.
I hope this helps
James
When I took Masters Organic Chemistry at SUNY Stony Brook “Mirror Image” Molecules were either Racemic or Stereoisomers. Regardless of the name the fact remains…When you Buy a Bottle of 1000mg of Vitamin E which is D,L- Tocopherol Acetate half passes through the Body Unchanged. Useless…BUT if separated the cost of Vitamin E would cost close to the GDP of a small country.
Great this has taught me. Thanks.
OK, thanks Nabulime.