AS & A-Level Chemistry 15 — Aromatic chemistry and advanced mechanisms

Organic chemistry is organised around functional groups, which are specific atoms or bonds within a molecule that determine its chemical reactions and physical properties. For example, all acyl chlorides contain the $-\text{COCl}$ group, dictating their addition-elimination reactions, while amides feature $-\text{CONH}_2$. Organic molecules can be represented using various formula types. A general formula algebraically represents the entire homologous series. A structural formula unambiguously shows how atoms are joined (e.g., $\text{CH}_3\text{CH}_2\text{CONH}_2$), whereas a displayed formula explicitly draws every atom and every bond. Skeletal formulas provide a simplified representation where carbon atoms are implied at the vertices of zig-zag lines, and hydrogen atoms attached to carbons are omitted. Systematic IUPAC nomenclature relies on identifying the longest carbon chain containing the principal functional group. For the functional groups detailed at A Level, amides use the suffix '-amide', acyl chlorides use '-oyl chloride', and amino acids use the prefix 'amino-' with the suffix '-oic acid' (e.g., 2-aminopropanoic acid). Naming also extends to straight-chain esters and nitriles up to six carbon atoms (six plus six for esters and amides). For aliphatic cyclic molecules containing a single ring of up to six carbon atoms, the prefix 'cyclo-' is used. The additional A Level classes include arenes (an aromatic ring), halogenoarenes (halogen bonded directly to that ring), phenols ($\mathrm{OH}$ directly attached to the ring), acyl chlorides ($\mathrm{R-C(=O)-Cl}$), amines, amides and amino acids. An amine has nitrogen bonded to carbon groups without an adjacent acyl carbonyl; primary, secondary and tertiary amines have one, two and three carbon groups on nitrogen. An amide has nitrogen attached directly to the carbonyl carbon: $\mathrm{RCONH_2}$, $\mathrm{RCONHR'}$ or $\mathrm{RCONR'R''}$. An amino acid contains both amino and carboxyl groups; a simple alpha-amino-acid pattern is $\mathrm{H_2NCH(R)COOH}$. In skeletal formulas, show N, O, halogens and hydrogens attached to heteroatoms explicitly. Carbon-bound hydrogens are inferred by valency. These class patterns describe connectivity; they are not interchangeable molecular formulas. For the required ester and nitrile naming examples, keep the carbon chains unbranched; naming secondary and tertiary amines is not required by the table.