Reference—AS organic notation conventions

In the syllabus, X represents a halogen atom, while R and R′ represent an alkyl group or hydrogen where appropriate. These symbols show the reaction pattern without committing to one named molecule.

Read the notation together with the functional group: R–X is a halogenoalkane, R–OH an alcohol and R–COOH a carboxylic acid. R and R′ need not be identical, and X is not a variable element chosen after the equation.

The substitution pattern R–Br + OH⁻ → R–OH + Br⁻ describes many bromoalkanes. A specific example such as CH₃CH₂Br is one member of the general family.

Do not treat R as “any atom” or replace X by a whole molecule. The symbols have fixed structural meanings.