Skip to main content

Using pKa as a Measure of Leaving Group Ability

Learning Objective: To compare various groups on their ability to break off or 'leave' from a molecule and, in that process, classify them as good or bad leaving groups.

 

Prerequisite:

Chapter: Fundamentals of Organic Reactions

 

Sub-topic: Leaving Groups

 

Author's Note: Strength is a comparative measure, an analogy that extends even to organic chemistry. Perhaps the earliest recount of strength for acids was immediately after their discovery, arranging them according to their increasing ability to make a solution acidic. Leaving groups must also have a similar scale to measure their ability to cleave from a molecule. The pKa scale offers exactly that, as described in this article.

Using pKa as a Measure of Leaving Group Ability

 pKa scale measures an acid’s strength, the lower number indicating stronger acid. 

A strong acid will easily liberate H+ ions in solution and increase the solution’s acidity.  So, an acid molecule must have a good counterpart that enables the easier, faster liberation of H+ without it reattaching. Therefore, the counterpart known as the conjugate bases must be experts at stabilizing the negative charges of the anions......

 

Using pKa as a Measure of Leaving Group Ability

 

Subscribe to read how the pKa scale is handy for measuring the ability of leaving groups to depart from a molecule.

 

Fundamentals of Organic Reactions
Organic Chemistry - Drawing Structures, Concepts, and Examples

Sign Up for our Newsletters and Download the Sample Chapter -  Common Reaction Types 

A free sample of our course, Organic Chemistry Fundamentals 

Organic Chemistry Tutorials - CurlyArrows Premium

What is Organic Chemistry?

  • Introduction
  • Elements of a Chemical Reaction
  • Components of a Chemical Reaction

    Unlock Organic Chemistry

 

Atom

  • Size of an atom- The world belongs to the tiniest!
  • Power of Protons
  • Mass Number
  • Average Atomic Mass
  • Molecule and Molecular Mass
  • The Electrons- An Atom’s Reactive Component
  • Atomic Orbitals- s, p, d, f
  • Filing of Atomic Orbitals and Writing Electronic Configuration
  • Valence and Core Electrons- How to Determine

     Unlock Atom

 

Bonding In Atoms

  • Octet Rule - Introduction and Bonding
  • Limitations of Octet Rule
  • Ionic Bond- Introduction and Formation
  • Formation of Ionic Compound
  • Requirements for Ionic Bonding
  • Appearance and Nature of Ionic Compounds
  • Physical Properties of Ionic Solids- Conductance, Solubility, Melting Point, and Boiling Point
  • Covalent Bond - How it Forms
  • Covalent Bond - Why it Forms?
  • Covalent Bond - Bond Pair (Single, Double, Triple) and Lone Pair
  • Number of Covalent Bonds- Valency
  • Types of Covalent Bonds- Polar and Nonpolar
  • Metallic Bond - Introduction and Nature
  • Significance of Metallic Bonding
  • Impact of Metallic Bonding on the Physical Properties
  • Applications of Metallic Bonding
  • Difference Between Metallic and Ionic Bond

     Unlock Bonding in Atoms

 

Covalent Bond

  • Theories on Covalent Bond Formation
  • Valence Bond Theory- Introduction and Covalent Bond Formation
  • Valence Bond Theory- Types of Orbital Overlap Forming Covalent Bonds
  • Applications, Limitations, and Extensions of Valence Bond Theory
  • Hybridization- Introduction and Types
  • sp3 Hybridization of Carbon, Nitrogen, and Oxygen
  • sp2 Hybridization of Carbon, Carbocation, Nitrogen, and Oxygen
  • sp Hybridization of Carbon and Nitrogen
  • Shortcut to Determine Hybridization
  • The shape of sp hybrid orbital - Why is the lobe unequal?
  • VSEPR Theory- Introduction
  • Difference between Electron Pair Geometry and Molecular Structure
  • Finding Electron Pair Geometry and Related Shape
  • Predicting Electron-Pair Geometry and Molecular Structure Guideline
  • Predicting Electron pair geometry and Molecular structure - Examples
  • Finding Electron-Pair Geometry and Shape in Multicentre Molecules
  • Drawbacks of VSEPR Theory
  • Electron Wave Property, LCAO and MOT - Introduction
  • Linear Combination of Atomic Orbitals - Formation of Sigma and Pie bonds using MO Approach
  • The Energetics of Bonding and Antibonding Molecular orbitals
  • Conditions for the Valid Linear Combination of Atomic Orbitals  
  • Features of LCAO Theory
  • Finding the Electronic Configuration of Molecules using MO and Predicting Comparative Stability using Bond Order
  • Setting up the MO diagram for homonuclear diatomic molecules – Second Period Elements
  • Setting up the Molecular Orbital Diagram for Heteronuclear Diatomic Molecules
  • The Non-bonding Molecular Orbitals
  • Weakness of the Molecular Orbital Theory
  • Covalent bond Characteristics - Bond Length
  • Factors affecting Bond Length
  • How does Electron delocalization (Resonance) affect the Bond length?
  • Covalent bond Characteristics- Bond Angle
  • Factors affecting Bond Angle
  • Covalent bond Characteristics - Bond Order
  • How Bond Order Corresponds to the Bond Strength and Bond Length
  • Solved Examples of Bond Order Calculations
  • Covalent Bond Rotation
  • Covalent Bond Breakage
  • Covalent Bond Properties -Physical State, Melting and Boiling Points, Electrical Conductivity, Solubility, Isomerism, Non-ionic Reactions Rate, Crystal structure

     Unlock Covalent Bond

 

Electronic Displacement in a Covalent Bond

  • Electronegativity- Introduction
  • Factors Affecting Electronegativity- Atomic number, Atomic size, Shielding effect
  • Factors Affecting Electronegativity-s-orbitals, Oxidation state, Group electronegativity
  • Application of Electronegativity in Organic Chemistry
  • Physical Properties Affected by Electronegativity
  • Inductive effect - Introduction, Types, Classification, and Representation
  • Factors Affecting Inductive Effect- Electronegativity
  • Factors Affecting Inductive Effect- Bonding Order and Charge
  • Factors Affecting Inductive Effect- Bonding Position
  • Application of Inductive Effect- Acidity Enhancement and Stabilization of the counter ion due to -I effect
  • Application of Inductive Effect-Basicity enhancement and stabilization of the counter ion due to +I effect
  • Application of Inductive Effect-Stability of the Transition States
  • Application of Inductive Effect-Elevated Physical Properties of Polar Compounds
  • Is the Inductive Effect the same as Electronegativity?
  • Resonance - Introduction and Electron Delocalization
  • Partial Double Bond Character and Resonance Hybrid
  • Resonance Energy
  • Significance of Planarity and Conjugation in Resonance
  • p-orbital Electron Delocalization in Resonance
  • Sigma Electron Delocalization (Hyperconjugation)
  • Significance of Hyperconjugation
  • Resonance Effect and Types
  • Structure Drawing Rules of Resonance (Includes Summary)
  • Application of Resonance
  • Introduction to Covalent Bond Polarity and Dipole Moment
  • Molecular Dipole Moment
  • Lone Pair in Molecular Dipole Moment
  • Applications of Dipole Moment
  • Formal Charges - Introduction and Basics
  • How to Calculate Formal Charges (With Solved Examples)
  • Difference between Formal charges and Oxidation State

   Unlock Electronic Displacements in a Covalent Bond

 

Common Types of Reactions

  • Classification of common reactions based on mechanisms
  • Addition Reactions
  • Elimination Reactions (E1, E2, E1cb)
  • Substitutions (SN1, SN2, SNAr, Electrophilic, Nucleophilic)
  • Decomposition
  • Rearrangement
  • Oxidation-Reduction

     Unlock Common Types of Reactions

 

Drawing Organic Structures

  • Introduction
  • Empirical Formula
  • How to Calculate Empirical Formula from percentage composition and atomic masses
  • Related Numerical Problems - Finding Empirical Formula (Solved)
  • Molecular Formula
  • Numerical Problems related to finding molecular formula  (Solved)
  • How to calculate molecular formula from empirical formula and molecular masses
  • Hill Nomenclature - The Empirical and Molecular Formula Writing Rules
  • E/Z Nomenclature -  Structure Writing Rules for Substituted Alkenes
  • Kekulé
  • Condensed
  • Skeletal or Bond line
  • Polygon formula
  • Lewis Structures- What are Lewis structures and How to Draw
  • Rules to Draw Lewis structures- With Solved Examples
  • Lewis structures- Solved Examples, Neutral molecules, Anions, and Cations
  • Limitation of Lewis structures
  • 3D structure representation- Dash and Wedge line
  • Molecular models for organic structure representation- Stick model, Ball-stick, and Space-filling
  • Newman Projection- Introduction and Importance
  • How to Draw Newman Projections from Bond-Line Formula (5 step-by-step solved examples on alkane, substituted alkane, alkene, ketone, and cycloalkane)
  • Drawing Newman Projections to the Bond line Formula (solved examples)
  • Sawhorse Projection

     Unlock Drawing Organic Structures

 

Functional Groups in Organic Chemistry

  • What are functional groups?
  • Chemical and Physical Properties affected by the Functional Groups
  • Identifying Functional Groups by name and structure
  • Functional Group Categorization- Exclusively Carbon-containing Functional Groups
  • Functional Group Categorization- Functional Groups with Carbon-Heteroatom Single Bond
  • Functional Group Categorization- Functional Groups with Carbon-Heteroatom Multiple Bonds
  • Rules for IUPAC nomenclature of Polyfunctional Compounds
  • Examples of polyfunctional compounds named according to the priority order
  • Examples of reactions wherein the functional group undergoes transformations

     Unlock Functional Groups in Organic Chemistry

 

Structural Isomerism

  • Introduction
  • Chain Isomerism
  • Position Isomerism
  • Functional Isomerism
  • Tautomerism
  • Metamerism
  • Ring-Chain Isomerism

     Unlock Structural Isomerism

 

Intermolecular Forces

  • Ion-Dipole Interactions-Introduction and Occurrence
  • Factors Affecting the Ion-Dipole Strength
  • Importance of Ion-Dipole Interactions
  • Ion-Induced Dipole - Introduction, Strength and Occurrence
  • Factors Affecting the Strength of Ion-Induced Dipole Interactions
  • Ion-Induced Dipole Interactions in Polar Molecules
  • Vander Waals Forces -Introduction
  • Examples of Vander Waals' forces
  • Vander Waals Debye (Polar-Nonpolar) Interactions
  • Factors affecting the Strength of Debye Forces
  • Vander Waals Keesom Force - Introduction, Occurrence and Strength
  • Vander Waals London Force - Introduction, Occurrence, And Importance
  • Factors Affecting the Strength of London Dispersion Forces- Atomic size and Shape
  • Introduction, Occurrence and Donor, Acceptors of Hydrogen Bond
  • Hydrogen bond Strength, Significance and Types
  • Factors Affecting Hydrogen Bond Strength
  • Impact of Hydrogen bonding on Physical Properties- Melting and boiling point, Solubility, and State
  • Calculation of the Number of Hydrogen Bonds and Hydrogen bond Detection

     Unlock Intermolecular Forces

 

Physical Properties

  • Physical Properties- Introduction, Role of Intermolecular Forces
  • Physical State Change-Melting Point
  • Role of Symmetry, Role of Carbon numbers, Role of Geometry
  • Physical State Change-Boiling Point
  • Intermolecular Forces and their Effect on the Boiling Point, Role of Molecular Weight (Size), Molecular Shape, Polarity
  • Boiling Point of Special Compounds- Amino acids, Carbohydrates, Fluoro compounds
  • Solubility in Water
  • Density
  • Preliminary Qualitative Analysis of some Organic Compounds | Intensive Physical Property Measurements

     Unlock Physical Properties

 

Fundamentals of Organic Reactions

  • Types of Arrows Used in Chemistry
  • Curved Arrows in Organic Chemistry- with Examples
  • Electrophiles - Introduction, Identification and Reaction
  • Formation and Classification of Electrophiles- Neutral and Charged
  • Difference between Electrophiles and Lewis Acids
  • Nucleophiles - Identification and Role in a Reaction
  • Types of Nucleophiles- Lone Pair
  • Types of Nucleophiles- Pie Bond
  • Types of Nucleophiles- Sigma Bond
  • Periodic Trend and Order in Nucleophilicity
  • Introduction to Reactions Involving Nucleophiles
  • Nucleophile Reactions- Aliphatic Displacement type - SN1, SN2
  • Nucleophile Reactions- Acyl Displacement type
  • Nucleophile reactions- Aromatic Displacement type- Electrophilic, Nucleophilic
  • Addition Reactions- Electrophilic, Nucleophilic, and Acyl
  • Ambident Nucleophiles- Introduction and Formation
  • Ambident Nucleophile - Nature of the Substrate
  • Ambident Nucleophile- Influence of the Positive Counter Ions
  • Ambident Nucleophile- Effect of Solvent
  • Lone Pair - Introduction and Formation
  • Physical Properties Affected by the Lone Pair- Shape and Bond Angle
  • Physical Properties Affected by the Lone Pair- Hydrogen Bonding
  • Physical Properties Affected by the Lone Pair- Polarity and Dipole Moment
  • Chemical property affected by the Lone pair- Nucleophilicity
  • Leaving Group - Introduction and Nature
  • Good and Bad Leaving Group
  • Factors Determining Stability of the Leaving Groups- Electronegativity, Size, Resonance Stability
  • Using pKa as a Measure of Leaving Group Ability
  • Leaving Groups in Displacement Reactions
  • Leaving Groups in Elimination Reactions

     Unlock Fundamentals of Organic Reactions

 

Reactive Intermediates

  • Carbocation - Introduction, Nature, and Types
  • Formation of Carbocation
  • Stability of Carbocations- Inductive, Resonance, and Hyperconjugation
  • Other Structural Features Increasing Carbocation Stability
  • Structural Feature Decreasing Carbocation Stability
  • Fate of the Carbocation
  • General Carbocation Formation Reactions
  • Carbanion - Introduction, Nature, and Types
  • Formation of Carbanions
  • Carbanion Stabilization
  • Ease of Formation of Carbanion -Acidic proton
  • Fate of the Carbanion
  • Free Radical - Introduction and Types of Carbon-Centred Radicals
  • Structure of Carbon-Centred Free Radical
  • Formation of Radicals
  • Stability of the Carbon-Centred Radicals
  • Other Structural Feature Increasing Free Radical Stability
  • Comparing Free Radical Stability using Dissociation energies (D-H)
  • Fate of Free Radicals
  • Common Reactions Involving Carbon-Free Radicals

     Unlock Reactive Intermediates

 

Stereoisomerism - Conformation and Configurational Isomerism

  • Conformations in Organic Chemistry - An Introduction
  • How are Conformational Isomers Depicted
  • Open Chain and Closed Chain Conformations
  • Nomenclature related to sp3-sp3 and sp3-sp2 bond rotations
  • Conformational Analysis
  • Factors affecting the stability of conformers - Stabilizing Interactions |Hyperconjugation
  • Factors affecting the stability of conformers - Stabilizing Interactions | Intramolecular Hydrogen Bonding
  • Factors affecting the stability of conformers - Stabilizing Interactions | Dipole Minimizations
  • Factors affecting the stability of conformers - Destabilizing Interactions | Steric strain
  • Factors affecting the stability of conformers - Destabilizing Interactions | Torsional strain
  • Factors affecting the stability of conformers - Destabilizing Interactions | Angle strain
  • Importance of Conformational Analysis
  • Conformation in Compounds with Lone Pairs
  • Role of Solvents in Conformations
  • An Example of Conformation Dependent Reaction and Product Selectivity
  • Geometrical Isomerism - Introduction
  • Impact of cis-trans isomerism on physical properties
  • Impact of cis-trans isomerism on chemical reactions
  • Scope of Geometrical Isomerism in Biological Systems and Industrial Applications
  • E/Z Nomenclature in Substituted Alkenes
     

     Unlock Stereoisomerism