Alkanes and Cycloalkanes

Alkanes

Alkanes are saturated hydrocarbons. All carbon atoms are sp³ hybridized, and there are only σ-bonds.

General formula: CₙH₂ₙ₊₂.

Alkane	Formula	n
Methane	CH₄	1
Ethane	C₂H₆	2
Propane	propane C₃H₈	3
Butane	C₄H₁₀	4
Pentane	C₅H₁₂	5

By the formula: if n = 5, then C₅H₁₂ (number of H = 2n + 2).

Chemical properties

• Combustion: CO₂ and H₂O are formed.
• Substitution (halogenation, in light, radical mechanism): CH₄ + Cl₂ → CH₃Cl + HCl.
• Cracking, dehydrogenation, isomerization.

Cycloalkanes

General formula: CₙH₂ₙ.

• Cyclopropane, cyclobutane: the ring opens (addition).
• Cyclopentane and cyclohexane undergo substitution reactions like alkanes.
• When cyclohexane is dehydrogenated, benzene is formed.

Preparation and properties

• Al₄C₃ + 12H₂O → 3CH₄ + 4Al(OH)₃.
• CH₃COONa + NaOH → CH₄ + Na₂CO₃ (fusion).
• Wurtz: 2CH₃Cl + 2Na → C₂H₆ + 2NaCl.
• Konovalov reaction: nitration with dilute HNO₃.
• C₁-C₄ are gases, C₅-C₁₅ are liquids, and higher ones are solids. They are insoluble in water.