Organic Chemistry
Explore the chemistry of carbon-based compounds — from simple hydrocarbons to functional groups, systematic naming, and the reactions that power everyday life.
What is Organic Chemistry?
Organic chemistry is the study of compounds that contain carbon. Carbon is unique because it can form four covalent bonds, allowing it to build chains, rings, and complex 3D structures. Organic compounds make up fuels, plastics, medicines, food, and all living things.
4
Bonds carbon can form
~10 M
Known organic compounds
C, H, O, N
Most common elements
Carbon atoms bond to hydrogen, oxygen, nitrogen, halogens and other carbon atoms. The ability of carbon to bond to itself creates the enormous variety of organic molecules seen in nature and industry.
Hydrocarbons
Hydrocarbons contain only carbon and hydrogen atoms. They are the simplest organic compounds and the basis for naming all organic molecules. The main families are alkanes, alkenes, and alkynes.
Alkanes (saturated hydrocarbons)
All single bonds (C–C). General formula: CnH2n+2. Relatively unreactive.
Alkenes (unsaturated — one double bond)
Contain at least one C=C double bond. General formula: CnH2n. More reactive than alkanes.
Alkynes (unsaturated — one triple bond)
Contain at least one C≡C triple bond. General formula: CnH2n−2. Very reactive.
Carbon chain prefixes (IUPAC naming):
meth- (1) • eth- (2) • prop- (3) • but- (4) • pent- (5) • hex- (6) • hept- (7) • oct- (8)
Functional Groups
A functional group is a specific atom or group of atoms attached to the carbon skeleton that gives the molecule its characteristic chemical properties. The functional group determines how an organic molecule reacts.
| Family | Functional Group | Suffix | Example |
|---|---|---|---|
| Alcohol | –OH (hydroxyl) | -ol | ethanol (C2H5OH) |
| Carboxylic acid | –COOH | -oic acid | ethanoic acid (CH3COOH) |
| Ester | –COO– | -yl -anoate | ethyl ethanoate |
| Aldehyde | –CHO | -al | methanal (HCHO) |
| Ketone | C=O (internal) | -one | propanone (acetone) |
Key Organic Reactions
Combustion
Hydrocarbons burn in oxygen to produce CO2 and H2O. Complete combustion produces no soot; incomplete combustion produces carbon monoxide and carbon particles.
CH4 + 2O2 → CO2 + 2H2O
Addition Reactions (alkenes)
A small molecule adds across the C=C double bond. The double bond breaks and new atoms attach to both carbons. Used in making polymers.
CH2=CH2 + H2 → CH3CH3 (hydrogenation)
Esterification
A carboxylic acid reacts with an alcohol (with an acid catalyst) to form an ester + water. Esters are responsible for the fruity smells in foods and perfumes.
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Polymerisation
Many small monomer units join together to form a long polymer chain. Addition polymerisation uses alkene monomers (e.g., polyethylene from ethene). Used in plastics and synthetic fibres.
Key Vocabulary
| Term | Definition |
|---|---|
| Hydrocarbon | An organic compound containing only carbon and hydrogen atoms. |
| Functional group | An atom or group of atoms that gives an organic molecule its characteristic chemical properties. |
| Saturated | Contains only single C–C bonds; no double or triple bonds (e.g., alkanes). |
| Isomer | Molecules with the same molecular formula but different structural arrangements of atoms. |
Worked Examples
Name the compound C4H10.
Step 1: Identify the number of carbons. 4 carbons → prefix is but-.
Step 2: Check the formula. CnH2n+2 → 2(4)+2 = 10 → matches, so it is an alkane.
Step 3: Alkane suffix is -ane.
Answer: butane. It is used as a fuel in camping stoves and lighters.
Identify the functional group in CH3CH2OH and name the compound family.
Step 1: Look for the –OH group at the end of the chain. Yes, present.
Step 2: –OH is the hydroxyl functional group → compound belongs to the alcohol family.
Step 3: 2 carbons (eth-) + alcohol suffix (-ol) = ethanol.
Answer: Ethanol is an alcohol. It is found in alcoholic drinks and is used as a solvent and biofuel.
Write the complete combustion equation for propane (C3H8).
Step 1: Products of complete combustion are always CO2 and H2O.
Step 2: Write unbalanced: C3H8 + O2 → CO2 + H2O
Step 3: Balance C: place 3 in front of CO2. Balance H: 8H → 4H2O. Balance O: 3(2)+4 = 10O → 5O2.
Answer: C3H8 + 5O2 → 3CO2 + 4H2O
Knowledge Check
Select the correct answer for each question.
Question 1
Which of the following is a saturated hydrocarbon?
Question 2
What is the IUPAC name for CH3CH2CH2OH?
Question 3
Which type of reaction involves a small molecule adding across a C=C double bond?
Question 4
The –COOH functional group is characteristic of which organic compound family?
Question 5
Two compounds have the molecular formula C4H10 but different structural arrangements. These compounds are best described as:
Key Concepts Summary
- •Organic chemistry studies carbon-based compounds; carbon forms 4 bonds enabling enormous structural variety.
- •Hydrocarbons contain only C and H: alkanes (single bonds), alkenes (one double bond), alkynes (one triple bond).
- •IUPAC names use a prefix for chain length (meth-, eth-, prop-, but-...) and a suffix for the functional group (-ane, -ene, -ol, -oic acid).
- •Functional groups (–OH, –COOH, –COO–, –CHO) determine chemical reactivity.
- •Key reactions include combustion, addition (alkenes), esterification, and polymerisation.