- “Initial Tails” and “Final Heads”
- 3 Ways To Make OH A Better Leaving Group
- A Simple Formula For 7 Important Aldehyde/Ketone Reactions
- Acids (Again!)
- Activating and Deactivating
- Actors In Every Acid Base Reaction
- Addition – Elimination
- Addition Pattern 1 – Carbocations
- Addition pattern 2 – 3 membered rings
- Addition Reactions
- Aldehydes And Ketones – Addition
- Alkene Pattern #3 – The “Concerted” Pathway
- Alkyl Rearrangements
- Alkynes – 3 Patterns
- Alkynes: Deprotonation and SN2
- Aromaticity: Lone Pairs
- Avoid These Resonance Mistakes
- Best Way To Form Amines
- Bulky Bases
- Carbocation Stability
- Carbocation Stability Revisited
- Carboxylic Acids are Acids
- Chair Flips
- Cis and Trans
- Conjugate Addition
- Curved Arrow Refresher
- Curved Arrows
- Determining Aromaticity
- Diels Alder Reaction – 1
- Dipoles: Polar vs. Covalent Bonding
- E2 Reactions
- Electronegativity Is Greed For Electrons
- Electrophilic Aromatic Substitution – Directing Groups
- Elimination Reactions
- Enantiocats and Diastereocats
- Epoxides – Basic and Acidic
- Evaluating Resonance Forms
- Figuring Out The Fischer
- Find That Which Is Hidden
- Formal Charge
- Frost Circles
- Gabriel Synthesis
- Hofmann Elimination
- How Acidity and Basicity Are Related
- How Are These Molecules Related?
- How Stereochemistry matters
- How To Stabilize Negative Charge
- How To Tell Enantiomers From Diastereomers
- Hybridization Shortcut
- Imines and Enamines
- Importance of Stereochemistry
- Intermolecular Forces
- Intro to Resonance
- Ketones on Acid
- Kinetic Thermodynamic
- Making Alcohols Into Good Leaving Groups
- Markovnikov’s rule
- Mechanisms Like Chords
- Mish Mashamine
- More On The E2
- Newman Projections
- Nucleophiles & Electrophiles
- Nucleophilic Aromatic Substitution
- Nucleophilic Aromatic Substitution 2
- Order of Operations!
- Oxidation And Reduction
- Oxidative Cleavage
- Pi Donation
- Pointers on Free Radical Reactions
- Protecting Groups
- Protecting Groups
- Proton Transfer
- Putting it together (1)
- Putting it together (2)
- Putting it together (3)
- Putting the Newman into ACTION
- Reaction Maps
- Recognizing Endo and Exo
- Redraw / Modify
- Robinson Annulation
- Robinson Annulation Mech
- Sigma and Pi Bonding
- SN1 vs SN2
- sn1/sn2 – Putting It Together
- sn1/sn2/e1/e2 – Exceptions
- sn1/sn2/e1/e2 – Nucleophile
- sn1/sn2/e1/e2 – Solvent
- sn1/sn2/e1/e2 – Substrate
- sn1/sn2/e1/e2 – Temperature
- Strong Acid Strong Base
- Strong And Weak Oxidants
- Strong and Weak Reductants
- Stronger Donor Wins
- Sugars (2)
- Synthesis (1) – “What’s Different?”
- Synthesis (2) – What Reactions?
- Synthesis (3) – Figuring Out The Order
- Synthesis Part 1
- Synthesis Study Buddy
- Synthesis: Walkthrough of A Sample Problem
- Synthesis: Working Backwards
- The 4 Actors In Every Acid-Base Reaction
- The Claisen Condensation
- The E1 Reaction
- The Inflection Point
- The Meso Trap
- The Michael Reaction
- The Nucleophile Adds Twice (to the ester)
- The One-Sentence Summary Of Chemistry
- The Second Most Important Carbonyl Mechanism
- The Single Swap Rule
- The SN1 Reaction
- The SN2 Reaction
- The Wittig Reaction
- Three Exam Tips
- Tips On Building Molecular Orbitals
- Top 10 Skills
- Try The Acid-Base Reaction First
- Two Key Reactions of Enolates
- What makes a good leaving group?
- What Makes A Good Nucleophile?
- What to expect in Org 2
- Work Backwards
- Zaitsev’s Rule
A few days ago I mentioned how three reactions of alkynes were kind of “weird” – hydration, oxymercuration, and hydroboration.
Today, let’s dig into that a bit.
In each of these three reactions, we break a carbon-carbon Pi bond and form a carbon-oxygen single bond and a carbon hydrogen single bond.
In the case of hydration (H3O+) and oxymercuration (HgSO4, H2O) the addition is “Markovnikoff”.
In the case of hydroboration (1. BH3, 2. H2O2/NaOH) the reaction is “anti-Markovnikoff”.
So far so good.
Notice how we have an alkene attached to an alcohol? We call these species “enols”.
However, there’s an extra wrinkle to the chemistry of these compounds that is just touched on in Org 1. We go into it in a lot more detail in Org 2.
Enols don’t tend to be very stable. They exist in an equilibrium with a constitutional isomer (remember – same formula, different connectivity). If you move a proton from the O to the C, and break C-C (pi) and form C-O (pi), you get a different functional group – a carbonyl.
We call this the “keto” form.
And the transformation of the enol into the keto form goes by the name “tautomerism”.
Tautomerism is a spontaneous process. There’s little that can be done to stop it. What this means is that as soon as the enol is formed, it will be transformed into its more stable keto form.
What that means for each of the three species above, is that they will be converted into ketones (the first two) and an aldehyde (the last one).
So in the cases we went through here, oxymercuration and hydration are a way to make ketones from alkynes. And hydroboration is a way to make aldehydes from alkynes.
You probably haven’t learned many ways of making aldehydes/ketones yet (besides ozonolysis) so this should come in handy for synthesis problems if it’s given to you.
Thanks for reading! James
PS Note how we always start with a terminal alkyne in these examples? One end of the alkyne is bonded to C and one is bonded to H? If we don’t use a terminal alkyne in this process, both ends of the alkyne are “equally substituted”. So we can’t have Markovnikoff selectivity, we’ll end up getting a mixture of products.