Exercises: Nitrogen-containing compounds

The characteristic smell of fish is due to amines, compounds that can be thought of as ammonia, $\text{NH}_3$, in which a hydrogen atom has been replaced by a carbon chain. The figure shows this substitution.

1. a) Explain in your own words what a primary amine is.
2. b) Write the condensed structural formula of methylamine.
3. c) Indicate in your formula the functional group $-\text{NH}_2$, called the amino group.

Primary amines are named by adding the suffix "-amine" to the name of the alkyl group (or as alkanamines).

1. a) Name $\text{CH}_3\text{-CH}_2\text{-NH}_2$.
2. b) Write the condensed structural formula of propylamine (propan-1-amine).
3. c) How many carbon chains are attached to the nitrogen in both? Is that the reason they are called primary?

Classify these three nitrogenous compounds, stating which family each belongs to (amine, amide or nitrile), and indicate their functional group:

1. a) $\text{CH}_3\text{-CH}_2\text{-NH}_2$
2. b) $\text{CH}_3\text{-CONH}_2$
3. c) $\text{CH}_3\text{-CH}_2\text{-CN}$

Ethanamide (acetamide) is the simplest amide with two carbons, $\text{CH}_3\text{-CONH}_2$.

1. a) Indicate its functional group, the amide group $-\text{CONH}_2$.
2. b) Explain which two groups the amide group "merges".
3. c) Write the condensed structural formula of methanamide, the single-carbon amide.

Acetonitrile is a common solvent in analytical laboratories; its IUPAC name is ethanenitrile, $\text{CH}_3\text{-CN}$.

1. a) Indicate its functional group, the nitrile or cyano group, $-\text{C}\equiv\text{N}$.
2. b) Write the formula of propanenitrile, with one more carbon in the chain.
3. c) Taking into account the two previous names, deduce whether the carbon of the nitrile group is counted when naming the chain.

Caffeine in coffee, tea, and many soft drinks has the molecular formula $\text{C}_8\text{H}_{10}\text{N}_4\text{O}_2$, with four nitrogen atoms forming part of its rings.

1. a) How many atoms does its molecule have in total?
2. b) Which four elements make it up?
3. c) Plant compounds containing nitrogen with physiological effects are called alkaloids: explain why caffeine fits this description.

Paracetamol is an analgesic whose molecule has a benzene ring with two substituents: an $-\text{OH}$ group and an $-\text{NH-CO-CH}_3$ group.

1. a) Identify which two families of compounds those functional groups belong to.
2. b) Explain what it means for paracetamol to be a polyfunctional molecule.
3. c) Draw a diagram of the ring with both groups in your notebook and circle the amide group.

You can do it on paper and send a photo with your answer.

Match each name with its formula, writing down the three correct pairs:

1. a) Ethylamine, propanenitrile, methanamide.
2. b) $\text{CH}_3\text{-CH}_2\text{-CN}$, $\text{H-CONH}_2$, $\text{CH}_3\text{-CH}_2\text{-NH}_2$.

The position of the amino group is also indicated with a locant.

1. a) Name $\text{CH}_3\text{-CH(NH}_2\text{)-CH}_3$.
2. b) Write the condensed structural formula of butan-1-amine.
3. c) Explain what the number in the name of an amine indicates and why ethylamine does not need one.

Butan-1-amine and butan-2-amine have the same molecular formula, $\text{C}_4\text{H}_{11}\text{N}$.

1. a) Write the condensed structural formulas of both.
2. b) What type of isomers are they? Justify your answer.
3. c) Draw their displayed formulas in your notebook.

You can do it on paper and send a photo with your answer.

Amides are named by replacing the "-oic" ending of the acid from which they derive with "-amide".

1. a) Write the condensed structural formulas of methanamide and propanamide.
2. b) Name $\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CONH}_2$.
3. c) Which acid does the name of the compound in part b) derive from? Write it down.

Butanenitrile is used as an intermediate in the synthesis of pharmaceuticals.

1. a) Write its condensed structural formula.
2. b) Name $\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CN}$.
3. c) Explain why the carbon of the $-\text{CN}$ group is numbered as carbon 1 of the main chain.

The proteins in your muscles are long chains of amino acids. The simplest is glycine, 2-aminoethanoic acid: $\text{NH}_2\text{-CH}_2\text{-COOH}$. The figure shows its displayed formula.

1. a) Indicate its two functional groups and name them.
2. b) Justify the name "amino acid".
3. c) Deduce its molecular formula.

A cup of black coffee contains about $97\ \text{mg}$ of caffeine, $\text{C}_8\text{H}_{10}\text{N}_4\text{O}_2$. Data: atomic masses $\text{C} = 12$, $\text{H} = 1$, $\text{N} = 14$, $\text{O} = 16$; $N_A = 6.022\times10^{23}\ \text{mol}^{-1}$.

1. a) Calculate the molar mass of caffeine.
2. b) Calculate how many moles of caffeine are in the cup.
3. c) How many caffeine molecules is that? Express the result in standard form to two significant figures.

Paracetamol, $\text{C}_8\text{H}_9\text{NO}_2$, contains an amide fragment in its structure, $-\text{NH-CO-CH}_3$, which derives from ethanoic acid.

1. a) Write the condensed structural formula of ethanamide and circle in your notebook the fragment it shares with paracetamol.
2. b) How many nitrogen and oxygen atoms does a molecule of paracetamol have?
3. c) Explain why paracetamol is said to be an amide derivative of ethanoic acid.

There are two bottles in the laboratory: one contains propanamide and the other propylamine.

1. a) Write the condensed structural formulas of both.
2. b) Write their molecular formulas and verify that they are not identical.
3. c) Explain why they are not isomers even though both have three carbon atoms and one nitrogen atom.

There are several amines with the molecular formula $\text{C}_3\text{H}_9\text{N}$.

1. a) Write and name the two possible primary amines.
2. b) What type of isomerism do they exhibit with respect to each other?
3. c) A third amine with this formula is ethylmethylamine, $\text{CH}_3\text{-CH}_2\text{-NH-CH}_3$: explain why it is not primary and state what type of amine it is.

Amides can be understood as carboxylic acids in which the $-\text{OH}$ group has been replaced by an $-\text{NH}_2$ group.

1. a) Write the condensed structural formulas of ethanoic acid and ethanamide and indicate the change.
2. b) Predict the name and condensed structural formula of the amide obtained from propanoic acid.
3. c) Explain, by comparing their molecular formulas, why an acid and its amide cannot be isomers.

Alanine is an amino acid involved in metabolism during physical exercise; its IUPAC name is 2-aminopropanoic acid.

1. a) Write its condensed structural formula.
2. b) Deduce its molecular formula.
3. c) Indicate its two functional groups, explain what the locant "2" indicates, and justify why the carboxyl group takes priority when numbering the chain.

The nylon in climbing ropes and technical clothing is a polyamide: a very long chain with many repeated $-\text{CO-NH}-$ groups.

1. a) Draw in your notebook a fragment of chain with two consecutive amide groups and circle them.

1. b) Explain what the prefix "poly-" means in polyamide.

1. c) Proteins are natural polyamides, formed by the joining of amino acids (for example, glycine, $\text{H}_2\text{N-CH}_2\text{-COOH}$). Relate the $-\text{CO-NH}-$ group in nylon to the link between two amino acids and explain what the bonds that join amino acids to one another are called.

You can do it on paper and send a photo with your answer.

A student writes in their notebook "propanamide: $\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-NH}_2$" and "methanenitrile: $\text{CH}_3\text{-CN}$".

1. a) Correct the first name and explain what is missing from that molecule for it to be an amide.
2. b) Correct the second name and explain the error in counting the carbon atoms.
3. c) Summarise in one sentence what to look for in a formula to distinguish an amine from an amide.

Propanenitrile and propanamide both have three carbon atoms, but belong to very different families.

1. a) Write the condensed structural formulas of both.
2. b) Write their molecular formulas and compare their composition.
3. c) Draw the displayed formula of propanenitrile in your notebook, showing the triple bond $\text{C}\equiv\text{N}$, and state how many bonds the nitrogen atom forms.

You can do it on paper and send a photo with your answer.

A paracetamol tablet contains $500\ \text{mg}$ of active ingredient, $\text{C}_8\text{H}_9\text{NO}_2$. Data: atomic masses $\text{C} = 12$, $\text{H} = 1$, $\text{N} = 14$, $\text{O} = 16$; $N_A = 6.022\times10^{23}\ \text{mol}^{-1}$.

1. a) Calculate the molar mass of paracetamol.
2. b) Calculate the number of moles of paracetamol in one tablet.
3. c) How many molecules does it contain? Express the result in standard form to two significant figures.
4. d) How many nitrogen atoms does that tablet contain? Justify your answer.

Urea, $\text{CO(NH}_2\text{)}_2$, was the first organic compound synthesised in the laboratory (Wöhler, 1828) and today is one of the most widely used nitrogen fertilisers in the world. Data: atomic masses $\text{C} = 12$, $\text{H} = 1$, $\text{N} = 14$, $\text{O} = 16$.

1. a) Draw its structure in your notebook, a carbonyl group with two $-\text{NH}_2$ groups attached to it, and explain why it can be considered a diamide derived from carbonic acid.
2. b) Calculate its molar mass.
3. c) Calculate the percentage by mass of nitrogen in urea and explain why it is so highly valued as a fertiliser.
4. d) Wöhler's synthesis overturned the idea that organic compounds could only be produced by living organisms: explain what this idea (the "vital force") consisted of and why the experiment was historic.

You can do it on paper and send a photo with your answer.

Unit challenge. How does organic structure determine the properties of the products you use every day? Become a chemical auditor in your home.

1. IUPAC inventory: Find three commercial products at home whose labels contain, respectively: a hydrocarbon (e.g., butane or paraffin alkanes), an oxygenated compound (e.g., ethanol or propanone), and a nitrogenous compound (e.g., urea or amines in cosmetics). Write their condensed structural formula and their official IUPAC systematic name.

2. Home experiment: Carefully place a drop ($V \approx 0.05 \pm 0.01\text{ mL}$) of rubbing alcohol and another of acetone-based nail polish remover onto a clean, non-absorbent surface. Measure the time for complete evaporation using your phone's stopwatch ($t \pm 0.2\text{ s}$), performing $3$ repetitions for each liquid at room temperature. Work in a well-ventilated area, away from flames, sparks or hot surfaces, use minimal amounts, avoid inhaling the vapours and contact with skin and eyes, and do it under adult supervision.

3. Data processing and comparison: Record the measurements in a table, calculating the mean value and its absolute uncertainty. Look up the molar mass and boiling point of the hydrocarbon from step 1 and of the two liquids from the experiment (ethanol and propanone) in the official NIST Chemistry WebBook portal. Plot a graph of boiling point versus molar mass and write a brief report explaining the observed trends based on polarity and intermolecular bonds.

Evaluation criteria:

• Rigorous accuracy in the formulation and IUPAC nomenclature of the three organic families.

• Appropriate processing of experimental data (means, uncertainties, clear table, and graph).

• Coherent scientific justification linking functional chemical structure to volatility and NIST data.