Hydrocarbons are compounds containing only carbon and hydrogen. They are classified into:
Saturated open-chain hydrocarbons. They are relatively unreactive (paraffins).
Conformations of Ethane: Eclipsed (least stable) and Staggered (most stable). Represented by Newman or Sawhorse projections.
Halogenation: Free radical substitution. (CH₄ + Cl₂ → CH₃Cl + HCl).
Wurtz Reaction: 2RX + 2Na (in dry ether) → R-R + 2NaX (Used to prepare higher alkanes with even number of carbon atoms).
Unsaturated hydrocarbons with at least one double bond. They show geometrical isomerism (cis-trans).
When an unsymmetrical reagent (like HBr) adds to an unsymmetrical alkene, the negative part of the reagent gets attached to the carbon atom of the double bond carrying the lesser number of hydrogen atoms.
Anti-Markovnikov's (Peroxide) Effect: In the presence of organic peroxides, addition of HBr to unsymmetrical alkenes goes against Markovnikov's rule.
Unsaturated hydrocarbons with at least one triple bond. The carbon atoms are sp hybridized. Terminal alkynes are acidic in nature due to the high s-character (50%) of the sp hybridized carbon.
Compounds containing at least one benzene ring. Benzene (C₆H₆) exhibits resonance, making it unusually stable.
A ring system is aromatic if it is planar, completely conjugated, and contains (4n + 2) π electrons (where n = 0, 1, 2...). Benzene has 6π electrons (n=1).
Electrophilic Substitution Reactions: Benzene undergoes nitration, halogenation, sulphonation, Friedel-Crafts alkylation, and acylation.