Isomers Alkenes and Alkanes

Alkanes

• Complete Combustion: Produces carbon dioxide (CO₂) and water (H₂O), yielding maximum energy efficiency. CnH2n+2+(1.5n+0.5)O2→nCO2+(n+1)H2OC_nH_{2n+2} + (1.5n + 0.5)O_2 \rightarrow nCO_2 + (n+1)H_2OCn​H2n+2​+(1.5n+0.5)O2​→nCO2​+(n+1)H2​O

• Incomplete Combustion: Occurs with limited oxygen, forming carbon monoxide (CO) or elemental carbon (C) along with water (H₂O), leading to reduced energy output and toxic byproducts.

Unsaturated Hydrocarbons

• Types:

  • Alkenes (CnH2n): Contain at least one double bond; used in synthesis and found in natural products.

  • Alkynes (CnH2n-2): Contain at least one triple bond; utilized in complex molecule synthesis.

  • Aromatic Compounds: Feature benzene rings; widely present in natural and synthetic materials.

• Reactivity: Higher than alkanes due to double or triple bonds, which participate in addition reactions.

Addition Reactions of Alkenes

1. Hydrogenation: Alkene reacts with H₂ in the presence of a metal catalyst (e.g., Pt, Pd, Ni), converting the double bond into a single bond.

2. Halogenation: Reaction with halogens (Cl₂, Br₂) forms dihalides.

3. Hydrohalogenation: Reaction with hydrogen halides (e.g., HCl, HBr, HI), following Markovnikov's rule.

4. Hydration: Addition of H₂O, often forming alcohols.

Isomers

• Constitutional Isomers: Same molecular formula but different atom connectivity.

• Stereoisomers: Same connectivity but different spatial arrangements (e.g., cis-trans isomers).