INTRODUCTION-

  • Catenation- Th ability of an element to form long chains or rings by bonding with atoms of the same elements.
  • Organic Chemistry- It is a branch of chemistry which study of carbon-based compounds. Organic compound obtained form plant and animals.
  • A Swedish chemist, Berzilius proposed Vital force which responsible for formation of organic compound. But in 1828, F. Wohler rejected this notation and he says that the we synthesised organic compound, urea from an inorganic compound, ammonium cyanate.
    • This reaction- NH4​OCN → NH2​CONH2​.
  • The synthesis of acetic acetic acid and methane after pioneering(repairing) by Kolbe(1845) and Berthelot(1856), hence they show that the organic compound can prepared from inorganic sources in laboratory.

CARBON ‘s TETRAVALENCE-

Tetravalence- Ability of an atom to form 4 bonds using its 4 valence electron. ex- C.

  1. SHAPES OF CARBON COMPOUNDS-
  • Some factor can affect the shape of carbon compounds-
    • Hybridization– It influence the bond length and bond enthalpy. The sp hybrid orbital contain more s character which cause closeness the nucleus and form strong and short orbital than sp3.
      • Also change in hybridization can affect the electronegativity or carbon.
    • Bonding- Single, double and triple bond affect bond angles and overall shape.
    • Electron Pair Repulsion- Lone and bond pairs repel each other, altering geometry according to the VSEPR theory.

2. CHARACTERISTIC FEATURE OF PIE(π) BOND-

  • Restricted rotation- Pi bond prevent free rotation around the double or triple bond, leading to fixed geometry.
  • Planar structure- Molecules of pi bond often have planar shape due to parallel overlap of p orbitals.
  • Bond length- Pi bond shorten bond length in double and triple bonds compared to single bonds, affecting molecular dimension.

STRUCTURAL REPRESENTATION OF ORGANIC COMPOUNDS-

  1. Complete, Condensed and Bond line Structural Formulas-

Types of Structural Formulas:

  • Organic compounds are represented using different structural formulas:
    • Lewis Structure: Shows all valence electrons using dots.
    • Dash Structure: Simplifies Lewis structures by using dashes for bonds.
      • Single dash (–): Single bond.
      • Double dash (=): Double bond.
      • Triple dash (≡): Triple bond.
      • Lone pairs may or may not be shown.
    • Complete Structural Formula: Focuses on all bonds and atoms explicitly.

2. Condensed Structural Formula:

  • Simplifies complete structures by:
    • Removing some or all bond dashes.
    • Using subscripts to show repeating groups.
    • Example: CH3CH2CH2CH2CH3 can be condensed to CH3(CH2)4CH3.

3. Bond-Line Structural Formula:

  • Simplifies further by:
    • Representing carbon-carbon bonds as zig-zag lines.
    • Omitting carbon and hydrogen atoms.
    • Only explicitly showing other atoms (e.g., O, N, Cl).
    • Terminals represent –CH3 groups, and line junctions represent carbon atoms bonded to hydrogens as needed.

4. Representation of Cyclic Compounds:

  • Cyclic compounds (e.g., cyclopropane, cyclopentane) are represented as polygons.

5. Three-Dimensional Representation:

  • Organic molecules can be depicted in 3D using:
    • Solid Wedge (▲): Bond coming out of the plane toward the observer.
    • Dashed Wedge (▼): Bond going behind the plane away from the observer.
    • Normal Line (—): Bonds lying in the plane of the paper.
  • Example: 3D representation of methane uses these conventions to illustrate its tetrahedral shape.

Classification of Organic Compounds

Organic compounds are classified based on their structures and functional groups. This helps in organizing the large number of existing compounds.

1. Classification Based on Structure:

I. Acyclic or Open-Chain Compounds:

  • Also known as aliphatic compounds.
  • Contain straight or branched chains of carbon atoms.

II. Cyclic or Closed-Chain Compounds:

  • Alicyclic Compounds:
    • Rings formed by carbon atoms.
    • These compounds resemble aliphatic compounds in properties.
    • Example: Cyclopropane, cyclohexane.
  • Aromatic Compounds:
    • Special ring structures with delocalized electrons.
    • Benzenoid Aromatics: Compounds with benzene-like structures (e.g., benzene, naphthalene).
    • Non-Benzenoid Aromatics: Compounds with aromaticity but without benzene rings (e.g., tropone).
    • Heterocyclic Aromatics: Aromatic rings containing atoms other than carbon (e.g., furan, thiophene, pyridine).

2. Classification Based on Functional Groups:

a) Functional Groups:

  • A functional group is an atom or group of atoms attached to a carbon chain that determines the compound’s chemical properties.
  • Examples:
    • Hydroxyl group (–OH).
    • Aldehyde group (–CHO).
    • Carboxylic acid group (–COOH).

b) Homologous Series:

  • A series of compounds with the same functional group and a common general formula.
  • Successive members differ by a –CH₂ unit.
  • Examples of homologous series:
    • Alkanes (CnH2n+2).
    • Alkenes (CnH2n).
    • Alkynes (CnH2n−2).
    • Alcohols, aldehydes, carboxylic acids, etc.

c) Polyfunctional Compounds:

  • Compounds containing two or more identical or different functional groups.
  • Example: Molecules with both –OH and –COOH groups.

Additional Insights for Competitive Exams:

  1. Aromaticity Rules (Hückel’s Rule):
    • A compound is aromatic if:
      • It is cyclic and planar.
      • It has (4n + 2) π-electrons, where n is a non-negative integer.
  2. Differences Between Aromatic and Alicyclic Compounds:
    • Aromatic: Delocalized π-electrons, stable, unique reactivity.
    • Alicyclic: Saturated or unsaturated rings, behaves like open-chain compounds.
  3. Reactivity Trends in Functional Groups:
    • Functional groups influence the physical and chemical properties of molecules.
    • Order of reactivity:
      • Electrophiles (e.g., –COOH) > Nucleophiles (e.g., –OH) > Neutral groups (e.g., –CH₃).
  4. Isomerism in Organic Compounds:
    • Structural Isomers: Differ in connectivity of atoms.
    • Stereoisomers: Same connectivity but different spatial arrangement.

IUPAC Nomenclature of Organic Compounds

  1. Introduction to Nomenclature
    • Organic chemistry involves millions of compounds, so a systematic naming method was developed by the IUPAC (International Union of Pure and Applied Chemistry).
    • The IUPAC system links names to structures, allowing the structure to be deduced from the name.
  2. Traditional Names (Trivial Names)
    • Before IUPAC, compounds were named based on origin or properties (e.g., citric acid from citrus fruits).
    • Trivial names, though non-systematic, are still used when systematic names are too long or complex.
  3. IUPAC Naming Basics
    • Hydrocarbons: Compounds with only carbon and hydrogen.
      • Saturated hydrocarbons (alkanes): Contain single bonds, e.g., methane (CH4).
      • Unsaturated hydrocarbons: Contain double or triple bonds (alkenes and alkynes).
    • Names are based on the structure and functional groups, with the longest chain of carbons forming the base name.
  4. Straight-Chain Alkanes
    • End with the suffix “-ane”.
    • Prefixes indicate the number of carbon atoms (e.g., methane, ethane).
  5. Branched Hydrocarbons
    • Chains attached to the main chain are alkyl groups (e.g., methyl, ethyl).
    • Alkyl groups are named by replacing the “-ane” in the alkane with “-yl”.
    • Branches are indicated with position numbers based on the parent chain.
  6. Rules for Naming Branched Alkanes
    • Identify the longest chain of carbon atoms as the parent chain.
    • Number the chain to give substituents the lowest possible numbers.
    • List substituents alphabetically. Prefixes like di-, tri-, etc., are used for multiple identical groups.
  7. Cyclic Compounds
    • Prefix “cyclo-“ is added before the name of the alkane.
    • Side chains are named as per the above rules.
  8. Functional Groups
    • A functional group determines the compound’s reactivity and naming priority.
    • Functional groups have specific suffixes or prefixes (e.g., alcohol (-ol), ketone (-one)).
    • Priority order affects numbering and naming (e.g., carboxylic acid > ketone > alcohol).
    • Polyfunctional compounds are named with the most important group as the suffix and others as prefixes.
  9. Substituted Benzene Compounds
    • Substituents are prefixed to benzene (e.g., methylbenzene).
    • For disubstituted benzene, positions are numbered to give the lowest possible numbers.
    • Relative positions can also be indicated as ortho (1,2), meta (1,3), or para (1,4).
  10. General Guidelines
    • Ensure the lowest numbering for substituents.
    • Combine prefixes, parent names, and suffixes systematically.
    • For compounds with double/triple bonds, indicate their position (e.g., hex-1-ene).

These principles create a clear and systematic framework for naming organic compounds.

Isomerism

  • Definition: Isomerism occurs when two or more compounds have the same molecular formula but different properties. These compounds are called isomers.
  • Types of Isomerism:
    • Structural Isomerism: Isomers differ in how atoms are bonded.
      • Chain Isomerism: Different arrangements of the carbon chain.
      • Position Isomerism: Different positions of functional groups or substituents.
      • Functional Group Isomerism: Different functional groups within the same molecular formula.
      • Metamerism: Different alkyl groups attached to the functional group.
    • Stereoisomerism: Isomers differ in spatial arrangements of atoms.
      • Geometrical Isomerism
      • Optical Isomerism

2. Organic Reaction Mechanisms

  • Substrate and Reagent:
    • Substrate: The molecule where the reaction occurs.
    • Reagent: The species interacting with the substrate.
  • Reaction Mechanism:
    • Involves breaking and forming covalent bonds.
    • A stepwise description includes electron movement, bond formation, and energetics.

3. Bond Cleavage

  • Heterolytic Cleavage:
    • Bond breaks unevenly, with both electrons going to one atom.
    • Produces ions: Carbocations (positively charged carbon species) and Carbanions (negatively charged carbon species).
    • Carbocations are stabilized by inductive and hyperconjugation effects.
  • Homolytic Cleavage:
    • Bond breaks evenly, with one electron going to each atom.
    • Produces neutral species called free radicals.

4. Electron Movement in Reactions

  • Shown using curved-arrow notation:
    • Arrow shows where electron pairs move.

5. Types of Reagents

  • Nucleophiles: Electron-rich species that donate an electron pair.
    • Examples: OH⁻, NH₃, CN⁻.
  • Electrophiles: Electron-deficient species that accept an electron pair.
    • Examples: Carbocations, molecules with polar bonds like carbonyl groups.

6. Electron Displacement Effects

  • Inductive Effect:
    • Electron density shifts through sigma bonds due to electronegativity differences.
    • Decreases with increasing bond distance.
  • Resonance Effect:
    • Delocalization of electrons in conjugated systems.
    • Increases molecule stability by distributing charge.

7. Resonance Structures

  • Definition: Multiple Lewis structures represent a molecule’s electronic structure.
  • Rules for Resonance Stability:
    • Structures with more covalent bonds and complete octets are more stable.
    • Negative charges on electronegative atoms and less separation of opposite charges increase stability.

8. Importance of Understanding Mechanisms

  • Helps predict reactivity, design synthetic strategies, and solve competitive exam problems.

This simplified summary focuses on key concepts, omitting examples and diagrams, to help strengthen basic understanding.

Resonance Effect

  • Definition: Interaction of π-bonds or a π-bond with a lone pair in adjacent atoms, creating polarity in molecules.
  • Types:
    1. Positive Resonance Effect (+R): Electron transfer is away from a substituent, increasing electron density at certain positions.
    2. Negative Resonance Effect (-R): Electron transfer is toward the substituent, reducing electron density.

Electromeric Effect (E Effect)

  • Definition: Temporary effect where π-electrons shift completely under the influence of an attacking reagent, reversed when the reagent is removed.
  • Types:
    1. Positive (+E): Electrons move toward the atom the reagent attaches to.
    2. Negative (-E): Electrons move away from the atom the reagent attaches to.

Hyperconjugation

  • Definition: Stabilization by delocalizing σ-electrons of C-H bonds attached to unsaturated systems or empty p orbitals.
  • Effect: Provides stability to carbocations and alkenes; more alkyl groups lead to greater stability.

Purification of Organic Compounds

  • Methods:
    1. Sublimation: Separates sublimable solids from non-sublimable impurities.
    2. Crystallization: Separates solids based on solubility differences.
    3. Distillation:
      • Simple Distillation: Separates liquids with different boiling points.
      • Fractional Distillation: For liquids with close boiling points.
      • Distillation under Reduced Pressure: For high boiling or easily decomposed liquids.
      • Steam Distillation: For steam-volatile compounds.
    4. Differential Extraction: Uses immiscible solvents to extract compounds.
    5. Chromatography:
      • Adsorption Chromatography: Based on varying adsorption on stationary phases.
      • Types: Column chromatography and Thin Layer Chromatography (TLC).

Qualitative Analysis of Organic Compounds

  • Detection of Carbon and Hydrogen:
    • Carbon: Oxidized to CO₂ (turns lime water cloudy).
    • Hydrogen: Forms water (turns white copper sulfate blue).
  • Detection of Other Elements:
    • Nitrogen, sulfur, halogens, and phosphorus are identified using Lassaigne’s test by converting covalent forms into ionic forms through sodium fusion.

Test for Sulphur:

  1. Lead Acetate Test:
    • Add acetic acid and lead acetate to the sodium fusion extract.
    • A black precipitate of lead sulphide (PbS) confirms sulphur.
  2. Sodium Nitroprusside Test:
    • Adding sodium nitroprusside to the extract produces a violet color, indicating sulphur.
  3. Sulphur with Nitrogen:
    • If both sulphur and nitrogen are present, sodium thiocyanate forms, giving a blood-red color with iron ions.
  4. Excess Sodium Fusion:
    • Excess sodium during fusion decomposes thiocyanate into cyanide and sulphide, allowing standard tests for these ions.

Test for Halogens:

  1. Silver Nitrate Test:
    • Acidify the sodium fusion extract with nitric acid and add silver nitrate.
      • White precipitate (soluble in ammonium hydroxide) → Chlorine.
      • Yellowish precipitate (partially soluble) → Bromine.
      • Yellow precipitate (insoluble) → Iodine.
  2. Removal of Interference:
    • If nitrogen or sulphur is present, boil the extract with nitric acid to remove cyanide or sulphide before the test.

Test for Phosphorus:

  1. Heat the compound with an oxidizing agent (like sodium peroxide) to form phosphate.
  2. Treat with nitric acid and ammonium molybdate.
    • Yellow color or precipitate confirms phosphorus.

Quantitative Analysis:

  1. Carbon and Hydrogen:
    • Burn the compound with oxygen and copper(II) oxide.
    • Carbon → Carbon dioxide (absorbed by potassium hydroxide).
    • Hydrogen → Water (absorbed by anhydrous calcium chloride).
    • Use mass of water and carbon dioxide to calculate percentages.
  2. Nitrogen:
    • Dumas Method: Heat the compound with copper oxide; collect nitrogen gas over potassium hydroxide.
    • Kjeldahl’s Method: Heat with sulfuric acid to convert nitrogen into ammonium sulfate, then release ammonia by adding sodium hydroxide. Titrate ammonia with sulfuric acid.
  3. Halogen (Carius Method):
    • Heat the compound with fuming nitric acid and silver nitrate in a Carius tube.
    • Weigh the silver halide (AgX) formed to calculate halogen percentage.
  4. Sulphur:
    • Oxidize sulphur to sulphuric acid and precipitate as barium sulfate using barium chloride.
    • Weigh barium sulfate to calculate sulphur content.
  5. Phosphorus:
    • Oxidize to phosphoric acid and precipitate as ammonium phosphomolybdate or magnesium pyrophosphate.
    • Use mass of the precipitate for phosphorus calculation.
  6. Oxygen:
    • Calculate by difference: 100% – sum of all other elements.
    • Direct method: Pass oxygen over red-hot coke, convert it to CO, then oxidize it to CO₂ using iodine pentoxide.

Key Concepts for Competitive Exams-

Practical Applications: Relate these methods to determining empirical and molecular formulas.

Basic Tests: Focus on the color changes and precipitates in qualitative tests.

Formulas: Learn the equations for calculating element percentages.

Methods: Understand the step-by-step processes of Dumas, Kjeldahl, and Carius methods.

Interferences: Know how to eliminate interfering substances for accurate tests.

These all are the notes of chapter 8 in chemistry. And after some time you get important questions and NCERT solutions HERE. *#THANKS FOR VISITIING, VISIT AGAIN#* 😊