Alkanes

Alkanes Definition and Classification

• Alkanes, also known as paraffins, are the simplest class of hydrocarbons, consisting only of carbon (C) and hydrogen (H) atoms with single covalent bonds.
• The general formula for alkanes is CnH2n+2.

Types of Alkanes

1. Straight-chain (Normal) Alkanes: Carbon atoms connected in a linear sequence without branches. Denoted as “n-” (e.g., n-pentane).
2. Branched-chain (Iso) Alkanes: Carbon atoms form a main chain with one or more branches. Denoted as “iso-” (e.g., isopentane).

Nomenclature

• The naming follows the IUPAC system:
  1. Identify the longest chain to determine the base name.
  2. Assign a prefix based on the number of carbons in the main chain (meth-, eth-, prop-, etc.).
  3. Add the suffix “-ane” to indicate an alkane.
  4. Identify and name any branches or substituents (methyl-, ethyl-, etc.).
  5. Number the carbon atoms in the main chain from the end nearest a substituent.
  6. Assign a number to each substituent and list them alphabetically before the base name.

Physical Properties

1. Molecular Size and Mass: Increase with more carbon atoms.
2. Boiling and Melting Points: Increase with size; branched alkanes have lower boiling points than their straight-chain counterparts.
3. Density: Increases with molecular mass but remains below 1 g/cm³.
4. Solubility: Insoluble in water, soluble in nonpolar solvents (hexane, benzene, chloroform).

Chemical Properties

1. Reactivity: Generally low due to stable C-C and C-H bonds.
2. Combustion: Burn in oxygen to produce CO2, H2O, and energy.
3. Halogenation: Undergo substitution reactions with halogens in UV light or heat.
4. Cracking: Broken down into smaller alkanes and alkenes with heat, pressure, or catalysts.
5. Isomerization: Can transform into different structural isomers.
6. Reforming (Aromatization): Converted into aromatic hydrocarbons and H2 gas with a catalyst (e.g., Pt).

Uses of Paraffins (Alkanes)

• Paraffins are widely used across industries due to their stability and non-reactivity:
  1. Fuels: Key components in gasoline, diesel, and kerosene for transportation, heating, and aviation.
  2. Lubricants: High molecular weight paraffins serve as lubricants for engines and machinery, reducing wear.
  3. Wax Production: Used in candles, wax paper, cosmetics, and protective coatings for perishables.
  4. Chemical Industry: Feedstocks for producing solvents, detergents, and plastics like polyethylene and polypropylene.
  5. Pharmaceuticals: Used as carriers or excipients in drugs to enhance delivery and effectiveness.

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