Quick questions on Amines and amides explained: HSC Chemistry Module 7

An amine has a nitrogen with at least one $N-H$ or $N-C$ bond and no carbonyl on that nitrogen. Classify by counting how many carbons are bonded to the nitrogen.

An amide has a nitrogen directly attached to a carbonyl carbon: $R-CO-NR'R''$. Classify by counting how many carbons are on the nitrogen (the same as amines, ignoring the carbonyl-attached carbon for classification purposes in many texts; HSC convention varies, but the safe call is to say "primary amide has $-CONH_2$, secondary has $-CONHR$, tertiary has $-CONR_2$").

The lone pair on nitrogen can accept a proton, making amines bases (analogous to ammonia):

An amide forms by condensation of a carboxylic acid with ammonia or an amine. The initial salt loses water on heating:

The amide linkage is the repeating unit in polyamides such as nylon 6,6 (made from 1,6-diaminohexane and hexanedioic acid) and proteins (made from amino acids). See the polymers dot point for full equations.

Small amines (up to about C4) are very soluble in water through hydrogen bonding. Aliphatic amines have a characteristic ammonia-like or fishy smell. Decaying flesh produces low-molar-mass amines such as putrescine ($H_2N(CH_2)_4NH_2$) and cadaverine ($H_2N(CH_2)_5NH_2$), responsible for the smell.

Classify each as a primary, secondary or tertiary amine: methylamine, dimethylamine, trimethylamine. State whether each can hydrogen bond. [3 marks]

Calculate the pH of a 0.10 mol L$^{-1}$ aqueous solution of methylamine, $K_b = 4.4 \times 10^{-4}$. [3 marks]

Ethanoic acid is reacted with methylamine to form an amide. (a) Write the structural equation. (b) Name the amide.