Organic Chemistry Class 12th Study Notes

Organic Chemistry – Class 12th Notes

Topics To Be Covered

  • HALOALKANES & HALOARENES

  • ALCOHOL, PHENOL & ETHER

  • ALDEHYDE, KETONES & CARBOXYLIC ACIDS

  • AMINES

  • BIOMOLECULES

Introduction to Basics

  • Organic Chemistry: The study of hydrocarbons and their derivatives.

    • Hydrocarbon: Compounds made exclusively of hydrogen and carbon (e.g., CH₄).

    • Halogen: Include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

Representation of Organic Compounds

  • Molecular Formula: e.g., C₄H₁₀ - represents the number of each type of atom present in a molecule.

  • Expanded Structural Formula: e.g., HHH
    CH₃-CH-CH₃ - shows all atoms and bonds explicitly.

  • Condensed Structural Formula: e.g., H₃C-CH₂-CH₂-CH₃ - provides a more compact representation.

  • Bond Line Notation:

    • Only shows C-C bonds, and assumes hydrogens are bound to carbons unless otherwise noted.

Hybridization and Bonds

  • Hybridization Types:

    • sp³ Hybridization: 4 sigma bonds; e.g., CH₄.

    • sp² Hybridization: 3 sigma bonds, 1 double bond; e.g., CH₂.

    • sp Hybridization: 2 sigma bonds, 1 triple bond; e.g., C₂H₂.

  • Lone Pairs (Lp): Lone pair electrons do not participate in bonding.

Introduction to Haloalkanes & Haloarenes

  • Definition: Compounds formed by the substitution of hydrogen atoms in hydrocarbons with halogen atoms.

    • Haloalkanes (Alkyl halides): Derived from aliphatic hydrocarbons (e.g., CH₃CH₂X).

    • Haloarenes (Aryl halides): Derived from aromatic hydrocarbons (e.g., C₆H₅X).

Classification of Haloalkanes

  1. Based on number of halogen atoms:

    • Monohaloalkane: 1 halogen.

    • Dihaloalkane: 2 halogens attached in various configurations.

    • Trihaloalkane: 3 halogens.

  2. Based on degree of carbon hybridization:

    • Primary (1°): sp³- hybridized (1 R-X bond).

    • Secondary (2°): sp³- hybridized (2 R-X bonds).

    • Tertiary (3°): sp³- hybridized (3 R-X bonds).

  3. Based on Structure:

    • Geminal: Both halogens attached to the same carbon.

    • Vicinal: Halogens attached to adjacent carbons.

  4. Specific Types:

    • Allylic Halides: Halogen is on carbon adjacent to a double bond.

    • Benzylic Halides: Halogen is attached to the carbon adjacent to a benzene ring.

    • Vinylic Halides: Halogen is bonded directly to the double-bonded carbon.

  5. Nomenclature:

  • IUPAC Naming: Includes counting the longest carbon chain, identifying and numbering substituents, and adding halogen prefix before the main name (e.g., 1-bromopropane).

Methods of Preparation of Haloalkanes

  1. From Alcohols:

    • Reacting alcohols with hydrogen halides (HX) to replace the -OH group with -X

$[R-OH + HX o R-X + H₂O]$

  1. From Hydrocarbons:

    • Free Radical Substitution (halogenation) in the presence of sunlight:

$[ CH₄ + Cl₂ o CH₃Cl + HCl]$

  1. From Alkyl Halides: Interaction with phosphorus halides (PX₃ or PX₅).

  2. Using NaBr and H₂SO₄:

    • Hydrolysis reactions with halogen exchange.

  3. From Dihalides: Through elimination reactions involving hydroxides or base-catalyzed reactions.

Physical Properties of Haloalkanes

  1. Boiling and Melting Points:

  • Higher than their parent hydrocarbons due to polar C-X bonds; the trend from RI > RBr > RCl > RF.

  1. Density: Denser than water; increases with halogen number and molecular mass.

  2. Solubility: Generally low solubility in water; more soluble in organic solvents.

  3. Color and Odor: Colorless in pure form; bromides and iodides may develop color upon exposure to light.

Chemical Properties of Haloalkanes

  1. Nucleophilic Substitution Reactions: Involve replacing a halogen atom with a nucleophile (SN1, SN2).

    • SN1 Mechanism: Two-step process involving carbocation formation.

    • SN2 Mechanism: One-step process with a backside attack leading to inversion of configuration.

  2. Elimination Reactions: Removal of HX to form alkenes from haloalkanes.

  3. Reaction with Metals: Formation of Grignard reagents or alkanes via Wurtz reaction.

Nomenclature of Alcohols, Phenols, and Ethers

  1. Alcohol:

    • General formula: R-OH.

    • IUPAC suffix: -ol (e.g., ethanol).

  2. Phenols:

    • Hydroxyl group directly on a benzene ring (e.g., phenol, o-cresol).

    • IUPAC naming includes the location of substituents on the aromatic ring.

  3. Ethers:

    • General formula: R-O-R'.

    • Naming involves naming the two alkyl groups followed by ‘ether’ (e.g., ethyl methyl ether).

Methods of Preparation and Properties of Alcohols

  1. Hydration of Alkenes:

    • Direct and indirect methods available (e.g., acid-catalyzed hydration).

  2. Reactions with Grignard Reagents:

    • Forming primary, secondary, and tertiary alcohols.

  3. Physical Properties:

    • Strong hydrogen bonding results in higher boiling points for alcohols compared to hydrocarbons.

  4. Chemical Properties:

    • Reactions with acids, metals, and other transformations such as oxidation and esterification.

Amines

  • Definition: Derivatives of ammonia (NH₃) where one or more hydrogens are replaced by organic groups.

  • Classification: Based on the number of alkyl groups bonded to nitrogen:

    • Primary (1°) - R-NH₂;

    • Secondary (2°) - R-NH-R';

    • Tertiary (3°) - R-N-R'.

  • Nomenclature: IUPAC names vary based on the structure (e.g., methylamine, diethylamine).

  • Physical Properties: Amines can form hydrogen bonds, leading to appreciable solubility in water, but solubility decreases with increased alkyl side-chain length.

  • Chemical Properties: Basic behavior makes them react with acids and they undergo alkylation and acylation reactions.

Special Reactions Involving Amines

  1. Hoffman Degradation: Converts amides to amines with one carbon less.

  2. Gabriel Synthesis: Used to synthesize 1° amines from phthalimide and alkyl halides.

Summary

These study notes cover a detailed understanding of various organic compounds such as haloalkanes, haloarenes, alcohols, phenols, ethers, and amines, their preparative methods, nomenclature, classifications, and properties, along with numerous chemical reactions relevant to these compounds in organic chemistry.