Hydrocarbons

Organic Chemistry - Hydrocarbons

Reactions Overview

Wurtz Reaction

  • Description: Combines alkyl halides with sodium in dry ether to produce higher alkanes.

  • Example: CH3Br+2Na+BrCH3→CH3−CH3+2NaBrCH_3Br + 2Na + BrCH_3 \rightarrow CH_3-CH_3 + 2 NaBr

Aromatization

  • Description: Heating n-alkanes with catalysts to yield benzene.

  • Example: Alkane →\rightarrow Benzene (773K, 10-20 atm).

Kolbe’s Electrolytic Method

  • Description: Electrolysis of sodium salt of carboxylic acid generates an alkane.

  • Example: 2CH3COONa→CH3−CH3+2CO2+2NaOH+H22CH_3COONa \rightarrow CH_3-CH_3 + 2 CO_2 + 2 NaOH + H_2

Isomerization

  • Description: Heating n-alkanes with AICI3 and HCl to create branched-chain alkanes.

  • Example: CH3(CH2)4CH3→3−MethylpentaneCH_3(CH_2)_4CH_3 \rightarrow 3-Methylpentane

Alkanes as Fuels

  • Description: Saturated hydrocarbons release energy when reacting with oxygen.

Boiling Point Effects

  • Description: Enhanced branching reduces boiling point due to lower surface area.

Conformations of Ethane

  • Staggered: More stable structure (less torsional strain).

  • Eclipsed: Less stable structure (more torsional strain).

Geometrical Isomerism

  • Requirements: Must have a double bond with two distinct groups on the doubly bonded carbons.

  • cis-Trans Isomers: The cis form has identical groups on the same side; the trans form on opposite sides.

  • Boiling Point: The cis isomer exhibits a higher boiling point.

Reactions of Alkenes

Oxidation Reactions

  • Cold Dilute KMnO4: Generates glycols from alkenes.

  • Ozonolysis: Addition of ozone forms carbonyl compounds, e.g., Pent-2-ene yields ethanal and propanal.

Acidic Behavior of Alkynes

  • Acidity Order: Ranges from Benzene < n-Hexane < Ethyne.

Aromatic Hydrocarbons

  • Aromaticity Conditions: Requires a planar structure, complete delocalization of π electrons, and (4n+2) π electrons.

  • Key Reactions: Involves Friedel Crafts, Nitration, Acylation, and Decarboxylation.