AS & A-Level Chemistry 07 — Organic foundations and hydrocarbons

Organic chemists use various types of chemical formulas to convey structural information. The general formula is an algebraic representation of a homologous series (e.g., $\mathrm{C_nH_{2n+2}}$ for alkanes). The molecular formula gives the exact number of each atom in a molecule, while the empirical formula shows the simplest whole$- \text{number}\,\text{ratio}$. A structural formula shows the unambiguous arrangement of atoms without necessarily drawing every bond (e.g., $\mathrm{CH_3CH_2OH}$), whereas a displayed formula explicitly draws every atom and every single bond. Skeletal formulas are simplified representations that omit carbon and attached hydrogen atoms from alkyl chains; only the carbon-carbon bonds are drawn as lines forming a zig-zag, with functional groups explicitly shown.

Systematic nomenclature provides a consistent way to name organic compounds. At AS Level, practise the specified simple aliphatic compounds with up to six carbon atoms, or six plus six for esters; ester and nitrile naming here is restricted to straight chains. Choose the appropriate parent chain containing the principal functional group; the carbon count gives the root name. The principal functional group determines the suffix, while alkyl branches or halogens are treated as prefixes. Give priority to the principal functional group when numbering. Halogenoalkanes and alcohols are further classified as primary $(1^{\circ})$, secondary $(2^{\circ})$ or tertiary $(3^{\circ})$ based on the number of alkyl groups attached to the carbon bonded to the functional group.