Organic reactions and everyday chemistry
Carbon compounds make up fuels, plastics, medicines, and living things. A few reaction types explain much of their chemistry.
Why carbon is special
Carbon forms four strong covalent bonds and links to other carbons in chains and rings, creating millions of compounds. Organic chemistry studies these compounds, from methane to DNA. Functional groups, specific groups of atoms, give molecules their characteristic reactions.
Hydrocarbons
Alkanes have only single bonds (\(\text{C}_n\text{H}_{2n+2}\)), such as propane in camping gas. Alkenes have at least one carbon-carbon double bond, such as ethene, which ripens fruit. Aromatic compounds like benzene have special stable rings. Hydrocarbons are the main components of fuels.
Functional groups
Alcohols contain \(-\text{OH}\) (ethanol); carboxylic acids contain \(-\text{COOH}\) (acetic acid in vinegar); esters contain \(-\text{COO}-\) and often smell fruity; amines contain nitrogen and are basic. Recognising functional groups predicts behaviour: alcohols and acids form hydrogen bonds and mix with water.
Addition reactions
Alkenes undergo addition: atoms add across the double bond. Ethene plus hydrogen (with a catalyst) gives ethane; ethene plus water gives ethanol. Adding bromine decolourises bromine water, a classic test for double bonds.
Substitution and esterification
In substitution, one atom or group replaces another. Esterification combines a carboxylic acid and an alcohol to make an ester and water, catalysed by acid. Esters give flavours and fragrances; the same chemistry makes polyester fibres.
Polymers
Polymers are long chains of repeating units (monomers). Addition polymers like polyethylene form when many ethene molecules link through their double bonds. Condensation polymers like nylon and polyester form with loss of small molecules such as water. Plastics, proteins, and DNA are all polymers.
Chemistry of life
Biological molecules are organic: carbohydrates store energy, lipids form membranes, proteins (polymers of amino acids) act as enzymes, and nucleic acids store genetic information. Cellular respiration, \(\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \to 6\text{CO}_2 + 6\text{H}_2\text{O}\), is a controlled combustion releasing energy in small steps.
Worked example
Identify the functional groups in aspirin: it has a carboxylic acid group and an ester group attached to a benzene ring. The ester can hydrolyse in water to form salicylic acid, which is why old aspirin can smell of vinegar (acetic acid is released).
Key takeaways
Carbon's four bonds create vast diversity. Hydrocarbons include alkanes, alkenes, and aromatics. Functional groups such as alcohols, acids, esters, and amines determine reactivity. Alkenes undergo addition; acids and alcohols form esters; monomers link into polymers. Life's chemistry is organic chemistry.
Flashcard
Chemistry of carbon compounds
Check your understanding
Which reaction converts an alkene into an alkane?