Introduction to Organic Chemistry

Two-part naming convention

• An organic compound's name has two parts: a stem (or prefix) and an ending (or suffix)
• The stem records the length of the longest continuous chain — how many carbons are joined end to end
• The ending tells you which functional group the molecule contains

Stems for the first six carbon-chain lengths

• These six are the only stems you need to recognise for IGCSE Chemistry

Endings for the homologous series in the IGCSE syllabus

Building a name from its stem and ending

• Two-carbon chain with all single bonds: eth-ane → ethane
• Two-carbon chain with a C=C: eth-ene → ethene
• Three-carbon chain with an –OH: prop-anol → propanol
• Four-carbon chain with a –COOH: but-anoic acid → butanoic acid

Numbering a functional group's position

• When a chain has more than two carbons, the functional group can sit on different carbons; numbering shows which
• Number the carbons starting from the end nearest the functional group
• Insert the number between the stem and the ending, separated by hyphens
• Example: propan-1-ol has the –OH on the first carbon (CH₃CH₂CH₂OH); propan-2-ol has the –OH on the middle carbon (CH₃CH(OH)CH₃)
• IGCSE questions usually need numbered names only for alcohols and alkenes where the choice of carbon matters

Naming polysubstituted molecules

• For two of the same functional group, attach a di- prefix to the ending and list the two carbon numbers separated by a comma
• Example: ethane-1,2-diol (the antifreeze used in car radiators) has an –OH on each of its two carbons (HOCH₂CH₂OH)