Exercises: Introduction to organic nomenclature: monofunctional compounds

Natural gas for cooking is methane, $\text{CH}_4$; tap water is $\text{H}_2\text{O}$; a lighter contains butane, $\text{C}_4\text{H}_{10}$; salt is $\text{NaCl}$ and rubbing alcohol is ethanol, $\text{C}_2\text{H}_6\text{O}$.

1. a) State which of these substances are organic compounds and which are not.
2. b) Explain in your own words which element is the "backbone" of organic chemistry.

Name these four hydrocarbons:

The figure shows the molecular models of all four.

1. a) $\text{CH}_4$
2. b) $\text{C}_2\text{H}_6$
3. c) $\text{C}_3\text{H}_8$
4. d) $\text{C}_4\text{H}_{10}$

1. e) Explain what the prefix (meth-, eth-, prop-, but-) indicates and what the suffix -ane indicates.

In a home there are three appliances that run on hydrocarbons: the boiler burns methane, a portable heater burns propane and the orange gas cylinder contains butane. Write the molecular formula of all three.

A camping stove gas canister contains butane, $\text{C}_4\text{H}_{10}$.

1. a) State how many carbon and hydrogen atoms its molecule has.
2. b) Which family of hydrocarbons does it belong to: alkanes, alkenes or alkynes?

Fruit naturally releases a gas that accelerates its ripening: ethene, $\text{C}_2\text{H}_4$.

1. a) What type of bond joins its two carbon atoms: single, double or triple?
2. b) Which family does it belong to?

In body repair shops, welding is done using acetylene blowtorches, whose IUPAC name is ethyne, $\text{C}_2\text{H}_2$.

1. a) What type of bond is there between its two carbon atoms?
2. b) Which family of hydrocarbons does it belong to?

Methanol, $\text{CH}_3\text{OH}$, is used as fuel in some model engines and ethanol, $\text{CH}_3\text{CH}_2\text{OH}$, is the alcohol in disinfectants.

1. a) What group of atoms do both formulas share?
2. b) What is this functional group called and which family do both compounds belong to?

The sour taste of vinegar is due to acetic acid, whose IUPAC name is ethanoic acid, $\text{CH}_3\text{COOH}$.

1. a) Count how many carbon, hydrogen and oxygen atoms its molecule has and write its molecular formula (all atoms together, without separating by groups).
2. b) Indicate in the formula the $-\text{COOH}$ functional group characteristic of carboxylic acids.

All alkanes follow the general formula $\text{C}_n\text{H}_{2n+2}$, where $n$ is the number of carbon atoms.

1. a) Check that this holds true for methane ($n = 1$) and for butane ($n = 4$).
2. b) Work out the molecular formula of the alkane with $5$ carbon atoms, called pentane.

Alkenes follow the general formula $\text{C}_n\text{H}_{2n}$ and alkynes, $\text{C}_n\text{H}_{2n-2}$.

1. a) Work out the molecular formula of propene (an alkene with $3$ carbon atoms).
2. b) Work out that of propyne (an alkyne with $3$ carbon atoms).
3. c) Explain why ethene cannot have the formula $\text{C}_2\text{H}_6$.

Two compounds with $4$ carbon atoms have formulas $\text{C}_4\text{H}_{10}$ and $\text{C}_4\text{H}_8$.

1. a) Using the general formulas, state which is an alkane and which is an alkene.
2. b) Name the alkane.
3. c) Could either of the two be an alkyne? Justify your answer using the general formula $\text{C}_n\text{H}_{2n-2}$.

Condensed structural formulas show the carbon chain, grouping each carbon atom with its hydrogens.

1. a) Write the condensed structural formula of ethane, propane and butane.
2. b) Describe in your own words how the chain grows when moving from one to the next.

Ethanol has the molecular formula $\text{C}_2\text{H}_6\text{O}$ and ethane, $\text{C}_2\text{H}_6$.

1. a) Explain why ethanol is not considered a hydrocarbon, even though it is so similar to ethane.
2. b) Which family does ethanol belong to and what is its functional group?

Indicate the functional group of each compound and state which family it belongs to:

1. a) $\text{CH}_3\text{OH}$
2. b) $\text{CH}_3\text{CH}_2\text{OH}$
3. c) $\text{CH}_3\text{COOH}$

An alcohol can be imagined as an alkane in which a hydrogen atom has been replaced by an $-\text{OH}$ group.

1. a) Apply this idea to methane and write the condensed structural formula of methanol.
2. b) Do the same with ethane and write that of ethanol.
3. c) Also write the molecular formulas of both alcohols.

In a home boiler, methane burns according to this chemical equation:

$\text{CH}_4 + 2\ \text{O}_2 \rightarrow \text{CO}_2 + 2\ \text{H}_2\text{O}$

The diagram shows the molecules involved in the reaction.

1. a) Count the carbon, hydrogen and oxygen atoms on each side of the arrow.
2. b) Explain what it means for the equation to be "balanced".

A student claims that there is a hydrocarbon with formula $\text{C}_2\text{H}_8$.

1. a) Use the general formula of alkanes, $\text{C}_n\text{H}_{2n+2}$, to show that this is impossible.
2. b) On the other hand, $\text{C}_3\text{H}_6$ does exist: which family does it belong to and how is it named? Justify your answer using the general formulas.

Butane and methylpropane have the same molecular formula, $\text{C}_4\text{H}_{10}$, but their condensed structural formulas are $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3$ and $(\text{CH}_3)_3\text{CH}$.

1. a) Draw both carbon chains in your notebook.
2. b) Explain what isomers are using this example.
3. c) Give reasons why, even though they contain the same total number of atoms, they are two different substances.

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

In the laboratory there are two bottles: one contains the alcohol with $2$ carbon atoms and the other contains the carboxylic acid with $2$ carbon atoms.

1. a) Write the condensed structural formula of each and name them according to IUPAC.
2. b) Circle the functional group in each formula and state its name.
3. c) State an everyday substance in which each one is found.

No one has ever seen a molecule of "methene" or "methyne".

1. a) Remember what type of bond defines alkenes and alkynes.
2. b) Reason why these bonds cannot occur in a single-carbon hydrocarbon.
3. c) What is, then, the smallest alkene that exists? And the smallest alkyne? Name them and write their formulas.

The bioethanol mixed with petrol at some petrol stations is ethanol, $\text{C}_2\text{H}_6\text{O}$.

1. a) Write its condensed structural formula and count how many atoms its molecule has in total.
2. b) Comparing it with ethane, $\text{C}_2\text{H}_6$, explain why both have $6$ hydrogens if ethanol also contains oxygen (hint: the $-\text{OH}$ group provides its own hydrogen).

Alcohols form an ordered series: methanol, $\text{CH}_4\text{O}$; ethanol, $\text{C}_2\text{H}_6\text{O}$; propanol, $\text{C}_3\text{H}_8\text{O}$.

1. a) Look at how the subscripts change and deduce the general formula of alcohols as a function of the number of carbon atoms $n$.
2. b) Predict the molecular formula of butanol, the alcohol with $4$ carbon atoms.
3. c) Check that your general formula also gives the correct result for ethanol.

If a butane heater burns with insufficient oxygen, $\text{CO}$, a very toxic gas, is formed instead of $\text{CO}_2$. The figure compares the two molecules.

1. a) Name both gases, $\text{CO}$ and $\text{CO}_2$, using prefix nomenclature.
2. b) Compare their formulas and explain why $\text{CO}$ is said to be the product of an "incomplete" combustion.
3. c) Explain what precaution you would take at home with gas heaters and why.

Guess the compound:

1. a) An alkene has $8$ hydrogen atoms per molecule. Deduce how many carbon atoms it has, write its molecular formula and name it.
2. b) An alkane also has $8$ hydrogen atoms. Deduce its formula and its name.
3. c) Check that both satisfy the general formulas $\text{C}_n\text{H}_{2n}$ and $\text{C}_n\text{H}_{2n+2}$, respectively.

Unit challenge. Become a chemical auditor of your home to decipher the composition and properties of everyday products.

1. Find four substances at home: a binary inorganic one (e.g., $NaCl$ or $H_2O_2$), a ternary one (such as $NaHCO_3$ or $NaClO$), and two monofunctional organic ones (ethanol and ethanoic acid in vinegar). Write their empirical/condensed structural formulas and name them according to IUPAC rules.

2. Using a syringe ($\pm 0,5\text{ mL}$) and a kitchen scale ($\pm 1\text{ g}$), measure the mass of increasing volumes ($10$, $20$, $30$, and $40\text{ mL}$) of water ($H_2O$) and rubbing alcohol (ethanol).

3. Construct a table with the measurements and uncertainties. Plot the graph of $m$ versus $V$ for both liquids and calculate their density from the slope of the best-fit line.

4. Prepare a short report that includes the nomenclature of the substances, the graph obtained, and a reasoned proposal linking density to the molecular structure of each compound.

Assessment criteria:

• Correctness and precision in inorganic and monofunctional organic IUPAC nomenclature.

• Rigorous treatment of experimental data, graphs, and measurement uncertainties.

• Quality of the analysis linking chemical formula and density.