PRELIMS

Carbon and Its Compounds

Carbon is a non-metal (atomic number 6, group 14) that exhibits unique properties such as Allotropy and Catenation.

Allotropes of Carbon

Substances with the same chemical properties but different physical properties.

1. Diamond:
   • Purest form of carbon; hardest natural substance.
   • Bad conductor of electricity/heat.
   • High refractive index (2.415); specific gravity (3.52).
   • Structure: Tetrahedral crystals with hybridisation.
   • Carbonado: Black diamonds containing graphite traces.
2. Graphite (Plumbago):
   • Soft, greasy, dark grey crystalline solid.
   • Good conductor of heat/electricity.
   • Structure: Hexagonal layer structure with hybridisation. Layers held by weak Van der Waals forces.
   • Uses: Lubricant, lead pencils, electrodes in electric furnaces, moderator in nuclear reactors.
3. Amorphous Carbon: Charcoal (Wood, Sugar, Bone), Coke (from Coal).
4. Fullerenes ( , Buckminsterfullerene): Spherical/cage-like molecules of carbon (football/soccer-ball shape); discovered 1985 (Nobel Prize 1996); soluble in organic solvents, unlike diamond/graphite.
5. Graphene: Single, one-atom-thick planar sheet of -bonded carbon atoms in a hexagonal lattice; extracted from graphite; extremely strong (~200× stronger than steel by weight), highly conductive; 2010 Nobel Prize in Physics (Geim & Novoselov); key material in next-gen electronics, batteries, and composites — an active R&D area in India's National Mission on Advanced Materials.
6. Carbon Nanotubes (CNTs): Cylindrical (tube-shaped) carbon structures rolled from graphene sheets; exceptional tensile strength and electrical conductivity; used in nanotechnology, composites, and electronics.

Functional Groups and IUPAC Naming Basics

• Functional Group: An atom or group of atoms that determines the characteristic chemical properties of an organic compound.
  • -OH (Hydroxyl): Alcohols (e.g., Ethanol, ).
  • -CHO (Aldehyde): e.g., Formaldehyde, Acetaldehyde.
  • -CO- (Ketone): e.g., Acetone.
  • -COOH (Carboxylic acid): e.g., Acetic acid.
  • -NH₂ (Amine): e.g., Aniline.
  • -X (Halogen: F, Cl, Br, I): Haloalkanes/Haloarenes.
• IUPAC Naming (Basics): Name = Prefix + Root word (parent chain) + Suffix.
  • Root word denotes number of carbons in the longest chain: Meth(1), Eth(2), Prop(3), But(4), Pent(5), Hex(6).
  • Suffix denotes the functional group/saturation: -ane (saturated, alkane), -ene (double bond, alkene), -yne (triple bond, alkyne), -ol (alcohol), -al (aldehyde), -one (ketone), -oic acid (carboxylic acid).

Hydrocarbons

Compounds of Carbon and Hydrogen only. Principal natural source is Petroleum.

1. Saturated (Alkanes/Paraffins): Single bonds between carbons. Relatively unreactive.
   • Formula: (e.g., Methane, Ethane).
2. Unsaturated: Double or triple bonds.
   • Alkenes: Double bonds ( ). Formula: (e.g., Ethene).
   • Alkynes: Triple bonds ( ). Formula: (e.g., Acetylene/Ethyne).
3. Aromatic: Cyclic compounds with alternating double bonds in a benzene ring. Have pleasant smell (Aroma).
   • Examples: Benzene, Naphthalene, Anthracene.

Polymerisation and Plastics

• Polymerisation: Conversion of small molecules (monomers) into macro-molecules (polymers).
• Plastics: Cross-linked polymers.
  1. Thermoplastics: Softened repeatedly on heating; hardened on cooling. (e.g., Polyethylene, Polystyrene, PVC, Teflon).
  2. Thermosetting Plastics: Permanent change on heating; once hard, cannot be reshaped. (e.g., Bakelite, Glyptal, Terrylene).
  • Bakelite: Phenol-formaldehyde resin; used in combs, electrical goods.

Rubber and Vulcanization

• Natural Rubber: Polymer of Isoprene; soft and sticky.
• Synthetic Rubber: Neoprene, Thiokol (chemically resistant; used in rocket fuel).
• Vulcanization: Process of heating natural rubber with Sulphur (or ) to increase strength and elasticity.

Fibres

• Synthetic Fibres: Polymers with strong intermolecular forces (Hydrogen bonding). Example: Nylon-6,6.
• Rayon: Synthetic fibre obtained from cellulose.

UPSC Relevance

Carbon chemistry is frequently tested for its environmental and industrial impact.

• Allotropes: Structural differences between Diamond and Graphite are classic conceptual questions; Graphene and Fullerenes are increasingly tested given their role in advanced materials and nanotechnology.
• Hydrocarbons: Natural gas (Methane) and LPG (Propane/Butane) contexts.
• Polymers: Differentiating between Thermoplastics (recyclable) and Thermosetting (durable) and the importance of Teflon (non-stick) or Bakelite.