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Introduction to organic chemistry

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Organic chemistry is the chemistry of carbon compounds. There are rules for writing their formulae and naming them.

Hydrocarbons and formulae

A hydrocarbon is a compound of hydrogen and carbon only.

Series, groups and isomers

A homologous series is a family with the same general formula and functional group, similar chemical properties, and a gradual trend in physical properties. Each member differs from the next by CH2.
A functional group is the atom or group of atoms that decides how a compound reacts (such as C=C or -OH).
Isomers have the same molecular formula but different structural formulae.

Naming and reaction types

Prefix (number of carbons): meth- 1, eth- 2, prop- 3, but- 4, pent- 5.
Suffix (series): -ane (alkane), -ene (alkene), -ol (alcohol), -oic acid (carboxylic acid).
Numbers show positions: but-1-ene has the double bond after carbon 1.
Reaction types: substitution (an atom is swapped, as in alkanes with halogens), addition (atoms add across a C=C), combustion (burning in oxygen).
Worked example

Name the alkane with three carbon atoms and give its molecular formula.

  1. Three carbons: prefix prop-.
  2. Alkane: suffix -ane.
  3. C_nH2n+2 with n = 3 gives C3H8.

Answer: Propane, C3H8

Key idea

Hydrocarbons contain only C and H. Know molecular, empirical, general, structural and displayed formulae. A homologous series shares a general formula and functional group. Isomers: same molecular formula, different structure. Prefixes meth, eth, prop, but, pent. Reactions: substitution, addition, combustion.

The interactive lesson includes the diagrams for this topic.

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