Topic 19: Organic Nitrogen Compounds: Amines, Amides, Amino Acids and Proteins

For a structural formula, show the atom connectivity in groups; for a displayed formula, show every bond; for a skeletal formula, omit carbon labels and carbon-bound H atoms but show N, O and their attached H atoms. Classify an amine as primary, secondary or tertiary by the number of carbon groups bonded directly to nitrogen.

Butylamine represents a primary aliphatic amine and phenylamine a primary aromatic amine. In both, the lone pair can bond to $\ce{H+}$, attack an electron-poor carbon, or donate to $\ce{Cu^{2+}}$; their different basicities change how readily protonation occurs.

A small amine mixes with water because its polar C-N/N-H region can form hydrogen bonds with water. The nitrogen lone pair accepts a hydrogen bond from water, and an N-H bond can donate one. These favourable amine-water attractions replace the attractions disrupted on mixing.

To make butylamine by reduction, begin with butanenitrile: $\ce{CH3CH2CH2CN}$ becomes $\ce{CH3CH2CH2CH2NH2}$. Count the nitrile carbon as part of the product chain.

Heat the aromatic nitro compound under reflux with tin and concentrated hydrochloric acid. Six reducing equivalents replace the two nitro oxygens by hydrogen, converting $\ce{-NO2}$ into $\ce{-NH2}$. In the acidic mixture the amine is initially present as an arylammonium salt; adding alkali liberates the free aromatic amine.

Thus nitrobenzene gives phenylamine. Preserve every other substituent on the ring when applying the route to a substituted nitroarene, and show the same carbon skeleton before and after reduction.

Alkali converts phenol into the more electron-rich phenoxide ion. Its activated ring couples mainly at the para position when that position is available, giving a conjugated azo compound; extended delocalisation absorbs visible light, so the product is coloured.

Ammonia attacks the electron-deficient carbonyl carbon of an acyl chloride; chloride is displaced and an amide forms. A second ammonia molecule neutralises the hydrogen chloride, so excess ammonia is used.

A primary amine reacts by the same acylation pattern to give an N-substituted amide. For example, ethanoyl chloride plus butylamine gives N-butylethanamide; an additional amine molecule accepts the released proton.

Each amino acid contains both $\ce{-NH2}$ and $\ce{-COOH}$. Condensation between these groups forms a peptide (amide) link and eliminates water; repeating the change produces a polypeptide or protein.

For propenamide, $\ce{CH2=CHCONH2}$ gives a backbone bearing $\ce{-CONH2}$ side groups. The poly(ethenol) repeat unit has $\ce{-OH}$ side groups on an addition-polymer carbon backbone.

For an addition polymer, open the monomer C=C to a C-C single bond, keep every substituent on its original carbon, place the smallest repeating section in brackets, and draw a bond through each bracket edge.

For a polyamide, remove the small-molecule fragments at complementary functional groups and join carbonyl carbon to nitrogen. Choose bracket boundaries so repeating the unit reconstructs the uninterrupted chain.

A soluble laundry bag or liquid-detergent capsule uses a poly(ethenol)-based film that is strong enough while dry but disperses or dissolves when water penetrates. Water forms hydrogen bonds to the many O-H groups and competes with polymer-polymer attractions.

Polyalkenes of similar molar mass have only London forces between chains, so separating their chains generally needs less energy than overcoming the hydrogen-bond network in a polyamide.

Use the same concentration, path length and wavelength when comparing optical rotations. In acid the cationic form is favoured; in alkali the anionic form is favoured.

Write a decision sequence before testing. For every branch record the reagent, concentration or heating condition, observation and inference. Use fresh portions so acid, alkali, silver ions or oxidants from one test cannot create a false result in the next; include a blank or known comparison when an observation is subtle.

Work on a microscale, wear eye protection, control heating and volatile reagents, and follow separate disposal routes for heavy-metal, silver, oxidising and organic waste. Unknowns must be treated as hazardous until identified.