Home / Infrared Spectroscopy: A Quick Primer On Interpreting Spectra
Infrared Spectroscopy: A Quick Primer On Interpreting Spectra
Last updated: October 31st, 2022 |
How To Interpret IR Spectra In 1 Minute Or Less: The 2 Most Important Things To Look For [Tongue and Sword]
Last post, we briefly introduced the concept of bond vibrations, and we saw that we can think of covalent bonds as a bit like balls and springs: the springs vibrate, and each one “sings” at a characteristic frequency, which depends on the strength of the bond and on the masses of the atoms. These vibrations have frequencies that are in the mid-infrared (IR) region of the electromagnetic spectrum.
We can observe and measure this “singing” of bonds by applying IR radiation to a sample and measuring the frequencies at which the radiation is absorbed. The result is a technique known as Infrared Spectroscopy, which is a useful and quick tool for identifying the bonds present in a given molecule.
We saw that the IR spectrum of water was pretty simple – but moving on to a relatively complex molecule like glucose (below) we were suddenly confronted with a forest of peaks!
Your first impression of looking at that IR might be: agh! how am I supposed to make sense of that??
To which I want to say: don’t panic!
Table of Contents
- Let’s Correct Some Common Misconceptions About IR
- Starting With “Hunt And Peck” Is Not The Way To Go
- IR Spectroscopy: The Big Picture
- The Two Main Things To Look For In An IR Spectrum: “Tongues” and “Swords”.
- Alcohols and Carboxylic Acids: More Detail
- Specific Examples of IR Spectra of Carbonyl Functional Groups
- Less Crucial, But Still Useful: Two More Very Diagnostic Areas.
- Glucose, Revisited: The 1 Minute Analysis
In this post, I want to show that a typical analysis of an IR spectrum is much simpler than you might think. In fact, once you learn what to look for, it can often be done in a minute or less. Why?
- IR is not generally used to determine the whole structure of an unknown molecule. For example, there isn’t a person alive who could look at the IR spectrum above and deduce the structure of glucose from it. IR is a tool with a very specific use. [Back in 1945 when IR was one of the few spectral techniques available, it was necessary to spend a lot more time trying to squeeze every last bit of information out of the spectrum. Today, with access to NMR and other techniques, we can do more cherry-picking]
- We don’t need to analyze every single peak ! (as we’ll see later, that’s what NMR is for : – ) ). Instead, IR is great for identifying certain specific functional groups, like alcohols and carbonyls. In this way it’s complimentary to other techniques (like NMR) which don’t yield this information as quickly.
With this in mind, we can simplify the analysis of an IR spectrum by cutting out everything except the lowest-lying fruit.
See that forest of peaks from 500-1400 cm-1 ? We’re basically going to ignore them all!
80% of the most useful information for our purposes can be obtained by looking at two specific areas of the spectrum: 3200-3400 cm-1 and 1650-1800 cm-1. We’ll also see that there are at least two more regions of an IR spectrum worth glancing at, and thus conclude a “first-order” analysis of the IR spectrum of an unknown. [We might write a subsequent post which gets nittier and grittier about the finer points of analyzing an IR spectrum]
Bottom line: The purpose of this post is to show you how to prioritize your time in an analysis of an IR spectrum.
[BTW: all spectra are from the NIST database. Thank you, American taxpayers!]
Confronted with an IR spectrum of an unknown (and a sense of rising panic), what does a typical new student do?
They often reach for the first tool they are given, which is a table of common ranges for IR peaks given to them by their instructor.
The next step in their analysis is to go through the spectrum from one side to the next, trying to match every single peak to one of the numbers in the table. I know this because this is exactly what I did when I first learned IR. I call it “hunting and pecking”.
The only people who “hunt and peck” as their first step are people who have no plan (i.e. “newbies”).
So by reading the next few paragraphs you can save yourself a lot of time and confusion.
[Hunt and peck has its place, but only AFTER you’ve looked for “tongues” and “swords”, below. Hunting and pecking is great to make sure you didn’t miss anything big – but as a first step, it’s bloody awful!]
In IR spectroscopy we measure where molecules absorb photons of IR radiation. The peaks represent areas of the spectrum where specific bond vibrations occur. [for more background, see the previous post, especially on the “ball and spring” model]. Just like springs of varying weights vibrate at characteristic frequencies depending on mass and tension, so do bonds.
Here’s an overview of the IR window from 4000 cm -1 to 500 cm -1 with various regions of interest highlighted.
An even more compressed overview looks like this: (source)
|3600 – 2700 cm-1||X-H (single bonds to hydrogen)|
|2700 – 1900 cm-1||X≡X (triple bonds)|
|1900 – 1500 cm-1||X=X (double bonds)|
|1500 – 500 cm -1||X–X (single bonds)|
Within these ranges, there are two high-priority areas to focus on, and two lesser-priority areas we’ll discuss further below.
When confronted with a new IR spectrum, prioritize your time by asking two important questions:
- Is there a broad, rounded peak in the region around 3400-3200 cm-1 ? That’s where hydroxyl groups (OH) appear.
- Is there a sharp, strong peak in the region around 1850-1630 cm-1 ? That’s where carbonyl groups (C=O) show up.
First, let’s look at some examples of hydroxyl group peaks in the 3400 cm-1 to 3200 cm-1 region, which Jon describes vividly as “tongues”. The peaks below all belong to alcohols. Hydrogen bonding between hydroxyl groups leads to some variations in O-H bond strength, which results in a range of vibrational energies. The variation results in the broad peaks observed.
Hydroxyl groups that are a part of carboxylic acids have an even broader appearance that we’ll describe in a bit.
[Sometimes it helps to know what not to look for. On the far right hand side is included one example of a very weak peak on a baseline that you can safely ignore.]
The main point is that a hydroxyl group isn’t generally something you need to go looking for in the baseline noise.
Although hydroxyl groups are the most common type of broad peak in this region, N-H peaks can show up in this area as well (more on them in the Note 1). They tend to have a sharper appearance and may appear as one or two peaks depending on the number of N-H bonds.
Next, let’s look at some examples of C=O peaks, in the region around 1630-1800 cm-1.. These peaks are almost always the strongest peaks in the entire spectrum and are relatively narrow, giving them a somewhat “sword-like” appearance.
That sums up our 80/20 analysis: look for tongues and swords.
If you learn nothing else from this post, learn to recognize these two types of peaks!
Two other regions of the IR spectrum can quickly yield useful information if you train yourself to look for them.
3. The line at 3000 cm-1 is a useful “border” between alkene C–H (above 3000 cm-1) and alkane C–H (below 3000 cm-1 ) This can quickly help you determine if double bonds are present.
4. A peak in the region around 2200 cm-1 – 2050 cm-1 is a subtle indicator of the presence of a triple bond [C≡N or C≡C] . Nothing else shows up in this region.
A Common Sense Reminder
First, some obvious advice:
- if you’re given the molecular formula, that will determine what functional groups you should look for. It makes no sense to look for OH groups if you have no oxygens in your molecular formula, or likewise the presence of an amine if the formula lacks nitrogen.
- Less obviously, calculate the degrees of unsaturation if you are given the molecular formula, because it will provide important clues. Don’t look for C=O in a structure like C4H10O which doesn’t have any degrees of unsaturation.
Let’s look at a specific example so we can see everything in perspective. The spectrum below is of 1-hexanol.
Note the hydroxyl group peak around 3300 cm-1 , typical of an alcohol (That sharp peak around 3600 cm-1 is a common companion to hydroxyl peaks: it represents non-hydrogen bonded O-H).
As you’d expect for 1-hexanol, there isn’t any telltale carbonyl peak around 1700 cm-1. Beginners might be tempted to label that dagger-like strong peak at about 1450 cm-1 as a possible C=O stretch. It is not. (it’s likely a C-H bend). Variations only occur within a very narrow range, and you are extremely unlikely to see a C=O stretch much below 1650 cm-1. The more spectra you see, the better you’ll get at making these judgements.
To gain some familiarity with variation, here’s some more examples of entire IR spectra of various alcohols.
Hydroxyl groups in carboxylic acids are considerably broader than in alcohols. Jon calls it a “hairy beard”, which is a perfect description. Their appearance is also highly variable. The OH absorption in carboxylic acids can be so broad that it extends below 3000 cm-1 , pretty much “taking over” the left hand part of the spectrum.
Here’s an example: butanoic acid.
Here’s some more examples of full spectra so you can see the variation.
The difference in appearance between the OH of an alcohol and that of a carboxylic acid is usually diagnostic. In the rare case where you aren’t sure whether the broad peak is due to the OH of an alcohol or a carboxylic acid, one suggestion is to check the region around 1700 cm for the C=O stretch. If it’s absent, you are likely looking at an alcohol.
[Note 1 for more detail on the 3200-3500 cm-1 region : Amines, Amides, and Terminal Alkynes]
The second important peak region is the carbonyl C=O stretch area at about 1630-1830 cm. Carbonyl stretches are sharp and strong.
Once you see a few of them they’re impossible to miss. Nothing else shows up in this region.
To put it in perspective, here’s the IR spectrum of hexanal. That peak a little after 1700 cm-1 is the C=O stretch. When it’s present, the C=O stretch is almost always the strongest peak in the IR spectrum and impossible to miss.
The position of the C=O stretch varies slightly by carbonyl functional group. Some ranges (in cm-1 ) are shown below:
- Aldehydes (1740-1690): benzaldehyde, propanal, pentanal
- Ketones (1750-1680): 2-pentanone, acetophenone
- Esters (1750-1735): ethyl acetate, methyl benzoate
- Carboxylic acids (1780-1710): benzoic acid, butanoic acid
- Amide (1690-1630): acetamide, benzamide, N,N-dimethyl formamide (DMF)
- Anhydrides (2 peaks; 1830-1800 and 1775-1740): acetic anhydride, benzoic anhydride
Conjugation will affect the position of the C=O stretch somewhat, moving it to lower wavenumber.
A decent rule of thumb is that you will never, ever see a C=O stretch below 1630. If you see a strong peak at 1500, for example, it is not C=O. It is something else.
- The C-H Stretch Boundary at 3000 cm-1
3000 cm-1 serves as a useful dividing line. Above this line is observed higher frequency C-H stretches we attribute to sp2 hybridized C-H bonds. Two examples below: 1-hexene (note the peak that stands a little higher) and benzene.
For a molecule with only sp3-hybrized C-H bonds, the lines will appear below 3000 cm-1 as in hexane, below.
2. The Distinctive Triple Bond Region around 2200 cm-1
Molecules with triple bonds appear relatively infrequently in the grand scheme of things, but when they do, they do have a distinctive trace in the IR.
The region between 2000 cm-1 and 2400 cm-1 is a bit of a “ghost town” in IR spectra; there’s very little that appears in this region. If you do see peaks in this region, a likely candidate is a triple bonded carbon such as an alkyne or nitrile.
Note how weak the alkyne peaks are. This is one exception to the rule that one should ignore weak peaks. Still, caution is required: if you’re given the molecular formula, confirm that an alkyne is possible by calculating the degrees of unsaturation and ensuring that it is at least 2 or more.
Terminal alkynes (such as 1-hexyne) also have a strong C-H stretch around 3400 cm-1 that is more strongly diagnostic.
OK. We’ve gone over 4 regions that are useful for a quick analysis of an IR spectrum.
- (important!) O-H around 3200-3400 cm-1
- (important!) C=O around 1700 cm-1
- C-H dividing line at 3000 cm-1
- (rare) Triple bond region around 2050-2250 cm-1
Now let’s go back and look at the IR of glucose. What do we see?
Here are the two big things to note:
- OH present around 3300 cm-1 . (in fact, this was included as one of the “swords” in section #3, above)
- No C=O stretch present. No strong peak around 1700 cm-1 . (The peak at 1450 cm-1 isn’t a C=O stretch).
Also, if we take a bit of extra time we can see:
- No alkene C-H (no peaks above 3000 cm-1 )
- Nothing in triple bonded region (rare, but still an easy thing to learn to check)
Now: If you were given this spectrum as an “unknown” along with its molecular formula, C6H12O6, what conclusions could you draw about its structure?
- The molecule has at least one OH group (and possibly more)
- The molecule doesn’t have any C=O groups
- The molecule *likely* doesn’t have any alkenes. If any alkenes are present, they don’t bear any C-H bonds, because we’d see their C-H stretch above 3000 cm-1.
A molecule with one degree of hydrogen deficiency (C6H12O6) but no C=O, and likely no C=C ?
A good guess would be that the molecule contains a ring. (We know this is the case, of course, but it’s nice to see the IR confirming what we already know).
This is what a 1-minute analysis of the IR of glucose can tell us. Not the whole structure, mind you, but certainly some important bits and pieces.
That’s enough for today. In the next post we’ll do some more 1-minute analyses and give more concrete examples of how to use the information in an IR spectrum to draw conclusions about molecular structure.
More on the 3200 region: Amines, Amides, and Terminal Alkyne C-H
While we’re in the 3200 region…. Amines and Amides
Amines and amides also have N-H stretches which show up in this region. [update: a comment from Paul Wenthold mentions some helpful advice about amides – they are rare – look for confirming evidence from the mass spectrum or other sources before assigning an amide based on a stretch in this region, as this region can also contain carbonyl “overtone” peaks]
Notice how the primary amine and primary amide have two “fangs”, while the secondary amine and secondary amide have a single peak.
The amine stretches tend to be sharper than the amide stretches; also the amides can be distinguished by a strong C=O stretch (see below).
Primary amines (click for spectra)
Terminal alkyne C-H
Terminal alkynes have a characteristic C-H stretch around 3300 cm-1. Here it is for ethynylbenzene, below.
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