Organic Chemistry (1)

Topic 11: Organic Chemistry

Overview

Organic chemistry is the branch of chemistry that studies carbon-containing compounds, focusing primarily on those derived from living organisms. It encompasses a vast range of substances, including natural and synthetic compounds, and it plays a crucial role in fields such as biochemistry, pharmacology, and materials science.

Hydrocarbons

Definition

Hydrocarbons are compounds consisting solely of carbon (C) and hydrogen (H) atoms, and they serve as the fundamental building blocks in organic chemistry.

Types

1. Saturated Hydrocarbons: These compounds contain only single bonds between carbon atoms. They are also known as aliphatic hydrocarbons.

   • General Formula: CₙH₂ₙ₊₂ (where n is the number of carbon atoms).

   • Example: Alkanes like Methane (CH₄) and Ethane (C₂H₆) are common examples.

2. Unsaturated Hydrocarbons: These contain at least one double or triple bond between carbon atoms, allowing for more complex structures and reactivity.

   • Alkenes (One double bond):

     • General Formula: CₙH₂ₙ.

     • Example: Ethylene (C₂H₄) is widely used in the production of plastics.

   • Alkynes (One triple bond):

     • General Formula: CₙH₂ₙ₋₂.

     • Example: Acetylene (C₂H₂) is utilized in welding and as a precursor for various organic compounds.

Alcohols

Definition

Alcohols are organic compounds characterized by the presence of a hydroxyl (-OH) functional group.

• General Formula: CₙH₂ₙ₊₁OH or CₙH₂ₙ₊₂O, depending on the structure.

Common Alcohols:

• Methanol (C₁H₄O): Used as a solvent and antifreeze, and as a fuel.

• Ethanol (C₂H₆O): Found in alcoholic beverages and used as a biofuel.

• Propanol (C₃H₈O): Utilized in hand sanitizers and as a solvent.

• Butanol (C₄H₁₀O): Used in the manufacture of plastics and as a solvent in various industrial processes.

Carboxylic Acids

Definition

Carboxylic acids are organic acids distinguished by the presence of a carboxyl (-COOH) functional group.

• General Formula: CₙH₂ₙ₊₁COOH or CₙH₂ₙO₂.

Common Carboxylic Acids:

• Methanoic acid (HCOOH): Also known as formic acid; used in tanning and as a preservative.

• Ethanoic acid (CH₃COOH): Known as acetic acid; used in vinegar and food preservation.

• Propanoic acid (C₃H₆O₂): Used as a food preservative and in the manufacture of antifungal agents.

• Butanoic acid (C₄H₈O₂): Has applications in food and as a chemical reagent.

Characteristics of Homologous Series

Members of the same homologous series exhibit the same functional group, leading to similar chemical properties. The series contains compounds that differ by a constant unit, such as a -CH₂- group.

• Example of Alkanes: Methane reacts with oxygen to yield carbon dioxide and water:

  • CH₄ + 2 O₂ → CO₂ + 2 H₂O

General Formula for Homologous Series:

• Alkanes: CₙH₂ₙ₊₂

• Alkenes: CₙH₂ₙ

• Alcohols: CₙH₂ₙ₊₁OH

• Carboxylic Acids: CₙH₂ₙ₊₁COOH

Consecutive Members: Differ by a -CH₂- group; this implies that each step in the series results in a new compound with distinct physical and chemical properties.

Physical Properties of Hydrocarbons

Generally, the boiling points of hydrocarbons rise with an increasing number of carbon atoms, though the incremental increase often decreases for longer carbon chains.

• Example:

  • Methane: -162°C (Gas)

  • Butane: 0°C (Gas)

  • Pentane: 36°C (Liquid)

Structural Isomers

Structural isomers are compounds that share the same molecular formula yet differ in the arrangement of atoms.

• Isomers of Butane (C₄H₁₀): Include Butane and 2-methylpropane, which have different physical and chemical properties despite having the same formula.

Rules for Naming Alkanes:

1. Identify the longest continuous carbon chain.

2. Identify and name any branches (e.g., methyl, ethyl).

3. Number the carbon atoms from the end nearest a branch, ensuring that the lowest numbers are assigned to branching points.

Fossil Fuels and Distillation

• Fossil Fuels: Include coal, petroleum, and natural gas, crucial energy sources.

• Fractional Distillation: A method utilized to separate crude oil into fractions based on varying boiling points.

• Fractions and their Boiling Ranges:

  • Refinery gas: C₁-C₄ (below 25°C)

  • Petrol: C₄-C₁₂ (40-100°C)

  • Kerosene: C₉-C₁₆ (150-240°C)

Reactions of Alkanes

Combustion:

• Complete Combustion: Yields carbon dioxide (CO₂) and water (H₂O), releasing energy efficiently.

• Incomplete Combustion: Produces carbon monoxide (CO) and water (H₂O), which can be hazardous due to CO toxicity.

Substitution Reactions:

Alkanes can react with chlorine in the presence of sunlight to produce chloroalkanes, showcasing their reactivity under certain conditions.

Reactions of Alkenes

Alkenes are generally more reactive than alkanes due to the presence of double bonds.

Addition Reactions:

• Hydrogenation: The addition of hydrogen across C=C bonds, converting them into C-C bonds.

• Reaction with Bromine water: Used as a test for unsaturation; alkenes decolorize bromine water.

• Hydration: Produces alcohols from alkenes when reacted with steam in the presence of an acid catalyst.

Comparison of Ethanol Production Methods

1. Fermentation: Involves the metabolic processes of yeast converting sugars into ethanol and carbon dioxide in an anaerobic environment.

2. Hydration: Involves the addition of water to ethene gas in the presence of a catalyst, producing ethanol efficiently.