Class 12 Chemistry Chapter 16 – Hydrocarbons Notes

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Chapter 17: Alkyl Halides and Amines

In Class 12 Chemistry, Chapter 17 covers two important classes of organic compounds: alkyl halides and amines. These compounds have significant industrial and biological importance, and understanding their properties, nomenclature, and reactions is crucial in organic chemistry.

Alkyl Halides (Haloalkanes)

  1. Introduction
  • Alkyl halides, also known as haloalkanes, are organic compounds in which one or more hydrogen atoms in an alkane are replaced by halogen atoms (fluorine, chlorine, bromine, iodine).
  1. Nomenclature
  • IUPAC Naming: The names are derived by adding the prefix of the halogen (fluoro-, chloro-, bromo-, iodo-) to the parent hydrocarbon name. The carbon chain is numbered to give the halogen the lowest possible number.
  • Common Naming: Often involves naming the alkyl group followed by the halide (e.g., methyl chloride, ethyl bromide).
  1. Classification
  • Primary (1°) Alkyl Halides: The carbon atom bonded to the halogen is attached to only one other alkyl group.
  • Secondary (2°) Alkyl Halides: The carbon atom bonded to the halogen is attached to two other alkyl groups.
  • Tertiary (3°) Alkyl Halides: The carbon atom bonded to the halogen is attached to three other alkyl groups.
  1. Physical Properties
  • Alkyl halides are generally colorless, with higher members being solids or liquids.
  • They have higher boiling points than the corresponding alkanes due to the presence of polar C-X bonds.
  • Solubility in water decreases with an increase in carbon chain length but is soluble in organic solvents.
  1. Chemical Properties
  • Nucleophilic Substitution Reactions: The most common reaction, where the halogen atom is replaced by a nucleophile (e.g., hydrolysis, cyanation, ammonolysis).
  • Elimination Reactions: Dehydrohalogenation to form alkenes.
  • Reactivity: The reactivity order of halides is RI > RBr > RCl > RF due to the bond dissociation energy.
  1. Uses and Importance
  • Alkyl halides are used as solvents, refrigerants, and in the synthesis of other organic compounds.

Amines

  1. Introduction
  • Amines are organic compounds derived from ammonia (NH₃) by replacing one or more hydrogen atoms with alkyl or aryl groups. They are categorized as primary, secondary, or tertiary depending on the number of alkyl or aryl groups attached to the nitrogen atom.
  1. Nomenclature
  • IUPAC Naming: The suffix -amine is used with the name of the parent hydrocarbon. The position of the amino group is indicated by a number (e.g., ethanamine, N-methylethanamine).
  • Common Naming: Based on the alkyl groups attached to the nitrogen (e.g., methylamine, dimethylamine).
  1. Classification
  • Primary (1°) Amines: One alkyl or aryl group attached to the nitrogen atom (R-NH₂).
  • Secondary (2°) Amines: Two alkyl or aryl groups attached to the nitrogen (R₂NH).
  • Tertiary (3°) Amines: Three alkyl or aryl groups attached to the nitrogen (R₃N).
  • Quaternary Ammonium Salts: Four groups attached to the nitrogen, carrying a positive charge (R₄N⁺X⁻).
  1. Physical Properties
  • Amines have distinct odors; lower aliphatic amines are gases, while higher ones are liquids or solids.
  • Amines can form hydrogen bonds, affecting their boiling points and solubility in water.
  • They are generally more soluble in water than hydrocarbons of similar molecular weight.
  1. Chemical Properties
  • Basicity: Amines are basic due to the lone pair of electrons on the nitrogen, which can accept a proton. The basicity depends on the nature of the alkyl groups attached.
  • Alkylation and Acylation: Amines can undergo alkylation and acylation to form higher amines or amides.
  • Reaction with Nitrous Acid: Primary aromatic amines react with nitrous acid to form diazonium salts, an important intermediate in the synthesis of azo dyes.
  1. Uses and Applications
  • Amines are used in the production of dyes, pharmaceuticals, surfactants, and rubber chemicals. They also play crucial roles in biological systems, such as neurotransmitters.

Alkyl halides and amines are versatile and widely used in both industrial applications and everyday products. Understanding their properties, reactions, and uses is essential for further studies and practical applications in organic chemistry and related fields.

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