Exercises: Oxygen-containing compounds

Surgical spirit is ethanol, $\text{CH}_3\text{-CH}_2\text{-OH}$, and methylated spirits contains methanol, $\text{CH}_3\text{-OH}$, which is highly toxic. The figure shows their displayed formulas.

1. a) Indicate the functional group that both molecules share.
2. b) What is this group called and which family do both compounds belong to?
3. c) Write the molecular formulas of methanol and ethanol.

In the laboratory there is a bottle labelled $\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-OH}$.

1. a) Name it according to IUPAC.
2. b) Write the structural formula of butan-1-ol.
3. c) What does the '1' in the name butan-1-ol indicate?

The acetone in nail polish remover has the IUPAC name propanone, $\text{CH}_3\text{-CO-CH}_3$. The figure shows its displayed formula.

1. a) Indicate its functional group, the carbonyl group $\text{C=O}$, and state which family it belongs to.
2. b) Reason why propanone does not need a number to indicate the position of the carbonyl group.
3. c) If the group $\text{C=O}$ were at the end of the chain, we would have $\text{CH}_3\text{-CH}_2\text{-CHO}$: which family would it belong to and what would it be called?

Formalin, used to preserve biological specimens, contains methanal, and vinegar owes its acidity to ethanoic acid.

1. a) Write the structural formula of methanal.
2. b) Write that of ethanoic acid.
3. c) Indicate and name the functional group of each one.

Ethoxyethane (formerly 'diethyl ether') was the first anaesthetic used in surgery, in 1846: $\text{CH}_3\text{-CH}_2\text{-O-CH}_2\text{-CH}_3$. The figure shows its structure.

1. a) Locate the oxygen atom and explain how it joins two carbon chains.
2. b) State which family it belongs to.
3. c) Deduce its molecular formula.

The pear flavor of many sweets is due to the ester ethyl ethanoate, $\text{CH}_3\text{-COO-CH}_2\text{-CH}_3$.

1. a) Indicate its functional group, the ester group $-\text{COO}-$.
2. b) Write its molecular formula.
3. c) Its name has two parts, 'ethanoate' and 'ethyl': state how many carbons each part contributes and locate them in the formula.

Isopropyl alcohol, which is used to clean screens and electronic components, is propan-2-ol, $\text{CH}_3\text{-CH(OH)-CH}_3$.

1. a) What does the '2' in its name indicate?
2. b) Write the structural formula of propan-1-ol.
3. c) Do both have the same molecular formula? Write it down.

Give the structural formulas for the following oxygen-containing compounds:

1. a) Ethanal, an intermediate in alcohol metabolism.
2. b) Methanoic acid, the substance injected by ants when they bite.
3. c) Butanone, a sweet-smelling solvent present in some glues.

The molecular formula $\text{C}_2\text{H}_6\text{O}$ corresponds to two very different substances: ethanol and methoxymethane, a gas used as an aerosol propellant.

1. a) Write the structural formulas of both.
2. b) Indicate the functional group of each one and state its family.
3. c) They are said to be functional group isomers: explain what this means.

Propanal and propanone share the molecular formula $\text{C}_3\text{H}_6\text{O}$.

1. a) Write the structural formulas of both.
2. b) How does the position of the carbonyl group differ in each one?
3. c) Reason why ethanal cannot have a ketone isomer. (Think about how many carbons are needed for the $\text{C=O}$ group to be in the middle of the chain.)

Butan-2-ol is an alcohol used as a paint solvent.

1. a) Write its structural formula.
2. b) Name the compound $\text{CH}_3\text{-CH(CH}_3\text{)-CH}_2\text{-OH}$.
3. c) Explain why in butan-2-ol it is necessary to indicate the position of the $-\text{OH}$ group, whereas in ethanol it is not.

In the laboratory, a pear flavouring is prepared by heating ethanoic acid with ethanol and a few drops of sulfuric acid:

$\text{acid} + \text{alcohol} \rightarrow \text{ester} + \text{water}$

1. a) Write the structural formulas of ethanoic acid and ethanol.
2. b) Write that of the ester formed, ethyl ethanoate.
3. c) Compare the formulas and explain where the atoms of the water molecule come from.

Ethyl methanoate (rum flavouring) and methyl ethanoate (present in the scent of some fruits) are two esters with the same molecular formula.

1. a) Write the structural formulas of both.
2. b) Indicate in each one which part comes from the acid and which from the alcohol.
3. c) Check that both are $\text{C}_3\text{H}_6\text{O}_2$ and explain why, despite this, they are different substances.

In IUPAC nomenclature, ethers are named using the prefix 'alkoxy-': the shorter chain attached to the oxygen is named as an alkoxy substituent and the longer one as an alkane.

1. a) Name $\text{CH}_3\text{-O-CH}_2\text{-CH}_3$.
2. b) Write the structural formula of ethoxypropane.
3. c) Explain what the prefix 'methoxy-' means.

Methanoic acid is the chemical defence of ants and the sting of nettles; propanoic acid (E-280) is used as a preservative in sliced bread.

1. a) Write the structural formulas of both acids.
2. b) Indicate the common functional group, the carboxyl group $-\text{COOH}$.
3. c) Butanoic acid, responsible for the smell of rancid butter, has one more carbon atom: write its molecular formula.

Butan-1-ol and butan-2-ol are solvents with molecular formula $\text{C}_4\text{H}_{10}\text{O}$.

1. a) Write the structural formulas of both.
2. b) What type of isomers are they: chain, position or functional group isomers? Reason your answer.
3. c) Also write the structural formula of a third isomer that is an ether and name it.

Three different compounds have the molecular formula $\text{C}_3\text{H}_6\text{O}_2$: one is a carboxylic acid and two are esters.

1. a) Write the structural formulas of all three and name them.
2. b) Indicate the functional group of each one.
3. c) The acid has an acidic taste and sour smell, and the esters smell fruity: relate these differences to their functional group and explain what functional group isomerism is.

Old chemical breathalysers detected ethanol in exhaled air by oxidising it: it is first converted into ethanal and then into ethanoic acid.

1. a) Write the structural formulas of the three compounds in the sequence.
2. b) Indicate the functional group and family of each one.
3. c) By comparing the formulas from one step to the next, explain which atoms are lost or gained and what 'to oxidise' means in organic chemistry.

An unlabelled bottle contains a compound with molecular formula $\text{C}_4\text{H}_{10}\text{O}$.

1. a) Propose two possible structures that are alcohols and name them.
2. b) Propose a structure that is an ether and name it.
3. c) Reason, using the general formula $\text{C}_n\text{H}_{2n+2}\text{O}$, why the compound cannot be an aldehyde or a ketone.

The food industry manufactures synthetic flavourings by esterification.

1. a) Break down the name 'ethyl ethanoate' into its two parts and explain which compound each part comes from.
2. b) Predict the name of the ester obtained from butanoic acid and ethanol (it is responsible for pineapple flavouring).
3. c) Write the structural formulas of butanoic acid, ethanol and the ester formed, and check by counting atoms that the reaction $\text{acid} + \text{alcohol} \rightarrow \text{ester} + \text{water}$ is balanced.

In an exam, a student names $\text{CH}_3\text{-CH}_2\text{-O-CH}_3$ as 'ethyl methyl ether' and $\text{CH}_3\text{-CH(OH)-CH}_3$ as 'propan-1-ol'.

1. a) The first name is an acceptable common name, but not systematic: write the IUPAC name.
2. b) The second name has a numbering error: correct it and justify your answer.
3. c) Explain the general rule applied when numbering a chain containing a functional group.

Banana flavouring is due to 3-methylbutyl ethanoate, an ester that is also manufactured for sweets.

1. a) Break down its name and deduce which acid and alcohol it comes from. (The alcohol 3-methylbutan-1-ol is $\text{CH}_3\text{-CH(CH}_3\text{)-CH}_2\text{-CH}_2\text{-OH}$.)
2. b) Write the structural formula of the ester.
3. c) Deduce its molecular formula and calculate its molar mass. Given atomic masses: $\text{C} = 12$, $\text{H} = 1$ and $\text{O} = 16$.

A ketone has 4 carbons in the main chain, the carbonyl group on carbon 2 and a methyl group on carbon 3.

1. a) Write its structural formula and name it.
2. b) Deduce its molecular formula and check that it satisfies $\text{C}_n\text{H}_{2n}\text{O}$, the same general formula as aldehydes.
3. c) Write the structural formula of an aldehyde isomer and name it.

Ethanol and methoxymethane are isomers with formula $\text{C}_2\text{H}_6\text{O}$ and yet their boiling points are $78\ \celsius$ and $-25\ \celsius$, respectively.

1. a) Check that both have the same molar mass. Given atomic masses: $\text{C} = 12$, $\text{H} = 1$ and $\text{O} = 16$.
2. b) Write their structural formulas and indicate the functional group of each one.
3. c) The $-\text{OH}$ group allows hydrogen bonds to form between neighbouring molecules whereas the ether group does not: use this idea to justify the huge difference in boiling points.