Give the systematic name of each of the following amines: (a) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\); (b) \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}\); (c) \(\mathrm{o}-\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{NH}_{2}\).

Understanding how to name primary amines is crucial for students tackling organic chemistry. A primary amine is characterized by a single alkyl or aryl group attached to the nitrogen atom.
To correctly name a primary amine, first identify the alkyl group. For example, in the molecule \textbf{methanamine} or \textbf{methylamine}, the methyl group (\textbf{CH}\(_3\)) is attached directly to the nitrogen atom (\textbf{NH}\(_2\)). The simplest way is to combine the name of the alkyl group with the word 'amine'.
Always remember that the alkyl groups are named in alphabetical order if more than one is present. In the given exercise, the correct name for the compound \textbf{CH}\(_3\)\textbf{NH}\(_2\) is methylamine, identifying it as a primary amine with a methyl group.

Moving on to secondary amines, the nomenclature includes recognizing two alkyl groups attached to the nitrogen. Secondary amines have the general formula \textbf{R}\(_1\)\textbf{R}\(_2\)\textbf{NH}, where \textbf{R}\(_1\) and \textbf{R}\(_2\) can be the same or different alkyl or aryl groups.
In defining the systematic name, you list both groups in alphabetical order, followed by 'amine'. The exercise presents a compound with two ethyl groups, \textbf{(CH}\(_3\)\textbf{CH}\(_2\))\(_2\)\textbf{NH}, which leads to the name diethylamine. The 'di' prefix indicates the presence of two identical alkyl groups. When the groups are different, each group is named separately, and you do not use prefixes like 'di', 'tri', etc.

Aniline derivatives form a special class in amine nomenclature. Aniline itself is the simplest aromatic amine, made of a phenyl group (\textbf{C}\(_6\)\textbf{H}\(_5\)) attached to an \textbf{NH}\(_2\) group. When other groups are substituted onto the benzene ring of aniline, you name the molecule by indicating the position and identity of the substituent.
For example, when a methyl group is added to the ortho position of aniline, as in \textbf{o-CH}\(_3\)\textbf{C}\(_6\)\textbf{H}\(_4\)\textbf{NH}\(_2\), it's named o-methylaniline, where 'o-' or ortho- indicates the position of the substituent relative to the \textbf{NH}\(_2\) group. This detailed and methodical approach helps eliminate ambiguity and provides a clear structure for identifying aniline derivatives.