Markovnikov’s rule
- “Initial Tails” and “Final Heads”
- 3 Ways To Make OH A Better Leaving Group
- A Simple Formula For 7 Important Aldehyde/Ketone Reactions
- Acetoacetic
- 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
- Amines
- 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
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- Conformations
- Conjugate Addition
- Curved Arrow Refresher
- Curved Arrows
- Decarboxylation
- Determining Aromaticity
- Diels Alder Reaction – 1
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- E2 Reactions
- Electronegativity Is Greed For Electrons
- Electrophilic Aromatic Substitution – Directing Groups
- Elimination Reactions
- Enantiocats and Diastereocats
- Enolates
- Epoxides – Basic and Acidic
- Evaluating Resonance Forms
- Figuring Out The Fischer
- Find That Which Is Hidden
- Formal Charge
- Frost Circles
- Gabriel Synthesis
- Grignards
- 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
- Hybridization Shortcut
- Hydroboration
- 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
- Paped
- Pi Donation
- Pointers on Free Radical Reactions
- Protecting Groups
- Protecting Groups
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- Putting it together (1)
- Putting it together (2)
- Putting it together (3)
- Putting the Newman into ACTION
- Reaction Maps
- Rearrangements
- 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
- Stereochemistry
- Strong Acid Strong Base
- Strong And Weak Oxidants
- Strong and Weak Reductants
- Stronger Donor Wins
- Substitution
- 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
- t-butyl
- Tautomerism
- 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
Going forward, there will be two big factors to keep in mind as you learn each addition reaction. “Regiochemistry” and”Stereochemistry”. Today, let’s talk about regiochemistry.
“Regiochemistry” [reeg-eee-o-chemistry] refers to how certain reactions end up forming one constitutional isomer over the other. Yesterday I said that every addition reaction involves breaking C-C (Pi) and forming a C-X and a C-Y bond. If X and Y are different atoms, then we have the potential to form two different constitutional isomers.
Many, many years ago, Viktor Markovnikoff noticed that when strong acids such as H-Cl add to alkenes, one type of product was preferred: the hydrogen added to the end of the double bond attached to the fewest carbons (“least substituted”) and the halide added to the end of the double bond attached to the most carbons (“most substituted”).
Important: he didn’t know why, at the time. He just made the observation that it happened. [This is how science works! We make observations first. Understanding “why” comes later.]
Let’s look.
In our example notice that C-2 of the alkene is attached to one H and one carbon (“R”), whereas C-1 of the alkene is attached to two hydrogens. So C-2 is the “most substituted” carbon. When we add H-Br to this alkene, the major product is the one where Br adds to C-2 (the “most substituted”) and the H adds to C-1 (the “least substituted”). This is “Markovnikoff’s rule”. (In this case we also get a small amount (~10-20%) of the opposite “regioisomer” – the “anti-Markovnikoff” product).
As we’ll see, certain reactions follow Markovnikoff’s rule. In others, Markovnikoff’s rule doesn’t operate, because the two atoms we’re adding to the alkene are exactly the same. Finally, there are even reactions (2 of them) in which the “anti-Markovnikoff” product is formed selectively.
A few days from now we’ll go into why Markovnikoff’s rule operates when we add HBr [as well as HCl, HI, and H3O(+)] to alkenes. For today, just make sure you can recognize which end of an alkene is the “most” and “least” substituted.
Bottom line: when you hear “regioselectivity”, think: “Markovnikoff or anti-Markovnikoff”.
Tomorrow: stereochemistry.
Thanks for reading! James