Organic compounds are chemical substances that contain carbon as their main element, combined mainly with hydrogen, oxygen, nitrogen, and other non-metals. The definition excludes simple carbon compounds such as carbon oxides (CO, CO₂), carbonates (CaCO₃), hydrogen carbonates (NaHCO₃), and carbides (CaC₂).

Key characteristics of organic compounds:

• Mostly covalent compounds (made of molecules)
• Have low melting and boiling points
• Most are insoluble in water but dissolve in organic solvents like ethanol or ether
• They are flammable
• They show isomerism (same molecular formula, different structures)

Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms. Aliphatic hydrocarbons are divided into three families based on the type of carbon-carbon bonds they contain.

2.1 Alkanes (Saturated Hydrocarbons)

Alkanes contain only single carbon-carbon bonds (C–C). They are called saturated hydrocarbons because each carbon atom is bonded to the maximum possible number of hydrogen atoms.

• General formula: CₙH₂ₙ₊₂ (where n = number of carbon atoms)
• Functional group: C–C single bond

Example: Pentane (C₅H₁₂) is a liquid used as a solvent in laboratories. Its carbon chain can be drawn as a straight chain or branched.

2.2 Alkenes (Unsaturated Hydrocarbons)

Alkenes contain at least one carbon-carbon double bond (C=C). They are called unsaturated because the double bond can be broken to add more atoms.

• General formula: CₙH₂ₙ (where n ≥ 2)
• Functional group: C=C double bond

Example: Ethene (C₂H₄) is a plant hormone used to ripen fruits. In Tanzania, bananas are often transported green and exposed to ethene gas to ripen them before market.

2.3 Alkynes (Unsaturated Hydrocarbons)

Alkynes contain at least one carbon-carbon triple bond (C≡C).

• General formula: CₙH₂ₙ₋₂ (where n ≥ 2)
• Functional group: C≡C triple bond

Worked Example:

Question: Write the molecular formula for butane, butene, and butyne, and identify which family each belongs to.

Solution:

• Butane: C₄H₁₀ (alkane family, formula CₙH₂ₙ₊₂)
• Butene: C₄H₈ (alkene family, formula CₙH₂ₙ)
• Butyne: C₄H₆ (alkyne family, formula CₙH₂ₙ₋₂)

Alcohols are organic compounds containing the hydroxyl functional group –OH attached to an alkyl group. The general formula is R–OH, where R is an alkyl group.

3.1 Homologous Series of Alcohols

• General molecular formula: CₙH₂ₙ₊₁OH or simply R–OH
• Successive members differ by one –CH₂– group

3.2 Nomenclature

Alcohols are named by replacing the "-ane" suffix of the corresponding alkane with "-anol."

• Ethane → Ethanol (C₂H₅OH)
• Propanol → Propanol (C₃H₇OH)
• Methanol → Methanol (CH₃OH)

3.3 Physical Properties

• Colorless liquids with characteristic odor (ethanol has a mild smell)
• Soluble in water (the smaller the molecule, the more soluble)
• Boiling points decrease as molecular size decreases
• Ethanol boils at 78°C

3.4 Chemical Reactions

a) Esterification (with carboxylic acids) Alcohol reacts with an acid to form an ester and water.

$C_2H_5OH + CH_3COOH \rightarrow CH_3COOC_2H_5 + H_2O$ (Ethanol + Ethanoic acid → Ethyl ethanoate + Water)

b) Reaction with electropositive metals Alcohols react with metals like sodium to produce alkoxides and hydrogen gas.

$2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2$

c) Oxidation Alcohols can be oxidized to carboxylic acids.

$C_2H_5OH \xrightarrow{[O]} CH_3COOH$ (Ethanol oxidized to Ethanoic acid)

d) Dehydration With concentrated sulfuric acid, alcohols lose water to form alkenes.

$C_2H_5OH \xrightarrow{H_2SO_4} CH_2=CH_2 + H_2O$ (Ethanol → Ethene + Water)

3.5 Production of Ethanol

Fermentation: Yeast breaks down sugars (from fruits, grains, or cassava) into ethanol and carbon dioxide.

$Glucose \xrightarrow{Yeast} Ethanol + Carbon\ Dioxide$

In Tanzania, traditional brewing often uses fermented cassava or maize to produce local alcoholic beverages.

Distillation: The fermented mixture is heated. Ethanol (boiling point 78°C) evaporates first and is condensed back into liquid, producing stronger drinks like spirits.

3.6 Uses of Ethanol

• As a solvent in paints, varnishes, and medicines
• As a fuel (biofuel additive in Tanzania)
• In alcoholic beverages (beer: 2–6% ethanol; wine: ~10% ethanol)
• As a sterilizing agent in hospitals
• In the production of other chemicals (e.g., trichloromethane)

Important safety note: Methanol is highly toxic. Ingestion of as little as 30 mL can cause blindness or death. Illegally distilled alcohols sometimes contain methanol contamination.

Isomers are compounds with the same molecular formula but different structural formulas. This occurs because carbon atoms can bond in different arrangements.

Example: Butane (C₄H₁₀) has two isomers:

• n-Butane: CH₃–CH₂–CH₂–CH₃ (straight chain)
• Isobutane: (CH₃)₃CH (branched chain)

These isomers have different boiling points and physical properties.

In Tanzania, organic chemistry is applied in everyday life through the brewing of traditional alcoholic beverages like busaa (from fermented maize or millet) and pombe. Understanding fermentation helps local brewers control the quality and alcohol content of their products. Additionally, petroleum refining—based on the separation of hydrocarbon fractions from crude oil—provides fuels like petrol and diesel used in Tanzania's transportation sector, with the Tanzania Petroleum Development Corporation (TPDC) playing a key role in processing these organic compounds for domestic use.