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Carbocation - Introduction, Nature, and Types

Learning Objective: To study carbocation as the reactive intermediate - formation, structure, and types.

Skill Level - Intermediate

 

Prerequisites: 

                      

Chapter: Reactive Intermediates

Sub-topic: Carbocation

 

Author's Note: Carbocations are electron-deficient and so, excellent electron acceptors. Many of the reactions in organic chemistry have carbocation intermediates as electrophiles and are involved in the formation of new covalent bonds. This section covers carbocation, its structure, the difference between a regular tetrahedral carbon and carbocation, and its types. 

Carbocation - Introduction, Nature, and Types

The cations are positively charged specie devoid of electrons; therefore, a carbocation is a carbon-containing cation.

A carbocation is a positively charged, electron-deficient carbon atom that functions as a reactive intermediate in many organic chemistry reactions. 

 

Difference between a normal, tetrahedral carbon and a carbocation

A carbon atom can form four covalent bonds by sharing its 4 valence electrons with another atom's valence electrons so that they both attain a stable valence shell electronic configuration of 8 through a hybridization process. 

The number 8 is the chemical rule of thumb....

However, the carbon atom in a carbocation has only 6 valence electrons....

The fourth position for 2 electrons is empty....

.

Types of Carbocations

Based on the number of alkyl substituents on the carbon, carbocations are of three types....

.

Subscribe to learn about carbocations, their structure, and their types.

Next: Formation of Carbocation

Next: Factors Stabilizing and Destabilizing the Carbocation

Next: Fate of the Carbocation

Next: General Carbocation Formation Reactions

 

Reactive Intermediates
Organic Chemistry - Drawing Structures, Concepts, and Examples

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What is Organic Chemistry?

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Atom

  • Size of an atom- The world belongs to the tiniest!
  • Power of Protons
  • Mass Number
  • Average Atomic Mass
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  • The Electrons- An Atom’s Reactive Component
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Bonding In Atoms

  • Octet Rule - Introduction and Bonding
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  • Ionic Bond- Introduction and Formation
  • Formation of Ionic Compound
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  • Covalent Bond - How it Forms
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  • Covalent Bond - Bond Pair (Single, Double, Triple) and Lone Pair
  • Number of Covalent Bonds- Valency
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  • Metallic Bond - Introduction and Nature
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Covalent Bond

  • Theories on Covalent Bond Formation
  • Valence Bond Theory- Introduction and Covalent Bond Formation
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  • 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
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  • 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?
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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

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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

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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

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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

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Structural Isomerism

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

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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

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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
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  • Solubility in Water
  • Density
  • Preliminary Qualitative Analysis of some Organic Compounds | Intensive Physical Property Measurements

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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

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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

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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
     

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