Introduction to Organic Chemistry (AQA A Level Chemistry)

Oleic acid is a fatty acid which occurs naturally in different animals and plants. It is also widely produced in industry, for its uses as an emulsifying agent and in the pharmaceutical industry. Figure 1 shows the structure of oleic acid.

Figure 1

i) State the type of formula oleic acid is represented by in Figure 1.

ii) Deduce the molecular formula of oleic acid.

iii) Draw the displayed formula of oleic acid. 

Oleic acid displays stereoisomerism. Figure 1 in part (a) shows one of the stereoisomers that oleic acid can exist as.

i) Define the term stereoisomerism.

ii) Apply the CIP priority rules to draw the skeletal formula of the second stereoisomer.

iii) Figure 2 below shows another fatty acid which is commonly found in milk. Explain why this compound does not display stereoisomerism.

Figure 2

Crotonic acid is another fatty acid which has a similar structure to oleic acid. The molecular formula of crotonic acid is C₄H₆O₂.

i) State the empirical formula of crotonic acid.

ii) Crotonic acid has a carboxylic acid functional group. Draw the displayed formula of the position and chain isomers of crotonic acid.

iii) Draw the cyclic functional group isomer of crotonic.

Two students, Student A and Student B, discuss the properties of oleic acid and crotonic acid.

Student A claims that both compounds belong to the same homologous series and Student B claims that both compounds have similar chemical properties.

Explain whether Student A, Student B or neither student is correct.

Crude oil consists of a mixture of hydrocarbons, which can be separated by fractional distillation. The shorter hydrocarbons are more useful as fuels such as gasoline and diesel fuel, so longer hydrocarbons are often converted into shorter ones in a       process called cracking. Cracking of hydrocarbons results in the formation of shorter alkanes and alkenes.

A hydrocarbon with molecular formula C₁₂H₂₄ is cracked to form oct-1-ene and one other alkene.

i) Write an equation for this cracking reaction.

ii) Draw the displayed formula of the functional group isomer and the position isomer of the second alkene formed in this reaction.

Figure 1 shows the reaction mechanism by which butene reacts with hydrogen bromide, to form compound X.

Figure 1

i) What does the curly arrow going from the C=C bond to the H in H-Br represent?

ii) State and explain the errors in the mechanism shown in Figure 1.

iii) Give the IUPAC name of compound X.

Compound X can also be formed from the reaction of butane with bromine.

CH₃CH₂CH₂CH₃ + Br₂ → CH₃CH₂CHBrCH₃ + HBr

i) State what type of reaction this is and the type of bond fission involved. 

ii) State which condition is required for the initiation step of this reaction.

iii) Write the equations for each of the following steps in the reaction of butane with bromine. There are multiple equations for the termination step, however only write the one that shows the formation of CH₃CH₂CHBrCH₃

Initiation step:                                                                 

Propagation step:                                        

Termination step: 

Once bromobutane has formed, further substitution can occur to form a compound with empirical formula C₂H₄Br.

Draw all the structural isomers of this compound.

A chemist is analysing a collection of organic compounds. The structural formulae of these compounds are shown in Table 1 below.

Table 1

Give the IUPAC name for the compounds to complete the table.

The scientist carried out some analytical research on his collection of compounds and found that some of these compounds display isomerism.

i) Identify the compounds which display chain isomerism and draw their isomers.

ii) State the empirical formula of compound 3.

iii) Explain whether compound 4 exhibits stereoisomerism.

The scientist carries out a synthetic reaction to form compound D from compound A as shown in the reaction sequence in Figure 1 below.

Figure 1

i) State the IUPAC names for compounds A-D

ii) Draw curly arrows in Figure 2 below to complete the mechanism for reaction 2.

Figure 2

iii) Draw all of the chain isomers of compound C while keeping the cyanide (CN) group in the same position.

Another compound in the scientist’s collection of organic compounds is shown in Figure 3 below.

Figure 3

This compound is the Z isomer. Which one of the labelled bonds leads to the prefix Z in the name? Explain your answer using CIP rules.

Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are widely used as solvents for dry cleaning, as refrigerants and as propellants for aerosols. 1,1,1,2,2-pentachloro-2-fluoroethane (CFC X) is an example of such CFCs.

Figure 1

State the IUPAC names of CFC Y and Z shown in Figure 1.

Unfortunately, CFCs are largely responsible for destroying the ozone layer. In the high atmosphere, the carbon-chlorine bonds break to give chlorine free radicals. It is these radicals which break down the O₃ and destroy the ozone layer. Figure 2 below shows the mechanism for this reaction.

Figure 2

i) State the type of reaction shown in Figure 2.

ii) The reaction in part (i) consists of three processes. Label each of the individual reactions in Figure 2 with the name of the correct process.

iii) State the error in the mechanism shown in Figure 2 and state the essential conditions needed for this reaction.

CFCs are now being replaced by less environmentally harmful compounds such as hydrofluorocarbons (HFCs). These compounds only contain hydrogen, carbon and fluorine atoms. Since they don’t contain a chlorine atom, they have no effect on the ozone layer.

An example of a HFC is a compound with molecular formula C₃H₅F₃.

Draw all the possible structural isomers of this compound.

Amines are often used in making azo-dyes and nylon apart from medicines and drugs.

Draw the skeletal formula for 4-bromo-5,6-dimethylheptan-2-amine.

This question is about the structure of organic compounds.

i) Draw the displayed formula of 2,3-dimethylpentanal.

ii) Draw the skeletal formula of compound X formed in Figure 1.

iii) State the empirical formula of the monochloro product formed in the free-radical substitution reaction between propane and chlorine.

Figure 2 shows the displayed formula of a type of fuel known as gasoline.

i) Give the IUPAC name of the compound shown in Figure 2.

Figure 2

ii) State the number of monochloro isomers which would be possible for the molecule in Figure 2.

iii) Draw the skeletal formulae of these monochloro isomers. Don't include chain isomers but only move the position of the chlorine atom.

Pent-1-ene (C₅H₁₀) is a member of the homologous series of alkenes. Pent-1-ene has structural isomers but no stereoisomers.

i) Define the term structural isomerism. 

ii) Give the IUPAC names of all possible functional group isomers of pent-1-ene.

iii) Draw the skeletal formula of the position isomers of pent-1-ene.

The structure of an alcohol X is shown in Figure 3.

Figure 3

i) Give the IUPAC name for alcohol X.

ii) What is the general formula of the homologous series of alcohols, which contain only one -OH group per molecule?

iii) State the empirical formula of alcohol X.

The characteristic smell of pine wood is due, partly, to the presence of a group of compounds called terpenes. One of the simpler terpenes is a compound called geraniol, which is an oily liquid at room temperature and pressure. The structure of geraniol is shown in Figure 1.

Figure 1

i) Deduce the molecular formula of geraniol. Use your answer to calculate the molar mass of geraniol in g mol⁻¹.

ii) Draw the displayed formula of geraniol.

Figure 2 shows the displayed formula of a type of fuel. 

i) Give the IUPAC name of the compound shown in Figure 2.

Figure 2

ii) State the number of monochloro isomers which would be possible for the molecule in Figure 2. 

iii) Draw the skeletal formulae of these monochloro isomers. Don’t include chain isomers but only move the position of the chlorine atom.

A compound with a molar mass of 72.0 g mol^-1 is composed of 66.63% C, 11.18% H, and 22.19% O.

i) State the number of structural isomers, containing a carbon-oxygen double bond, that this compound can form.

ii) Draw and name the skeletal formula of these isomers.

1,1,1,2-tetrafluoro-but-2-ene is another compound containing hydrogen, carbon and fluorine atoms.

i) State the meaning of the term stereoisomers and explain why 1,1,1,2-tetrafluoro-but-2-ene displays stereoisomerism. 

ii) Draw the E and Z isomers of 1,1,1,2-tetrafluoro-but-2-ene.

Ethers are a homologous series of organic compounds containing the R−O−R functional group.

The structures and names of two ethers are shown in Figure 1.

Figure 1

i) Draw the skeletal formula of the ether, 2-ethoxy-3-methylbutane.

ii) Determine the molar mass of 2-ethoxy-3-methylbutane.

Ethers can be prepared by nucleophilic substitution of haloalkanes with alkoxide ions, RO⁻.

Alkoxide ions can be prepared by reacting sodium with an alcohol. A gas is also formed.

Write an equation for the formation of methoxide ions from sodium and an alcohol.

Methoxyethane, shown in part (a), can be prepared by reacting bromoethane, CH₃CH₂Br, with methoxide ions, CH₃O⁻.

Outline the mechanism for the nucleophilic substitution of CH₃CH₂Br with CH₃O⁻ using skeletal formulae.

Your answer should include relevant charges, dipoles and the products formed.

i) In this mechanism, explain how CH₃O⁻ ions have acted as a nucleophile.

ii) A student commented that this is an example of homolytic fission. Using your knowledge of organic mechanisms, justify this statement.

Cisplatin is an effective intravenous anti-cancer drug. It exists in two stereoisomers cisplatin and transplatin, only cisplatin is effective as a chemotherapy treatment. Cisplatin exists as a square planar molecule with a platinum (Pd²⁺) central metal ion surrounded by two NH₃ and two Cl^- ions which act as ligands. Each ligand forms a coordinate bond with the platinum ion.

i) Draw the 3D representation of cisplatin including the bond angles.

ii) State the limitation of the cis-trans naming rules when it comes to the molecule shown in Figure 1.

iii) State the name of the molecule shown in Figure 1.

This question is about saturated hydrocarbons. Compound A is shown in Figure 2.

Figure 2 

The reaction of compound A with excess chlorine forms a compound D, which has a molar mass of 175.5 g mol⁻¹.

Draw a possible structure for compound D and write the equation for its formation from compound A. Use molecular formulae in the equation.

Butenedioic acid is HOOCCH=CHCOOH. It has two stereoisomers, commonly known as malic acid and fumaric acid. Both acids are responsible for the sour taste in fruit.

i) Draw the two E-Z isomers of butenedioic acid in skeletal formulae and label them as E-butenedioic acid and Z-butenedioic acid.

ii) State which part or parts of the molecule are responsible for the sour fruit taste. 

The hydrocarbon propane can be reacted with chlorine to prepare 2-chloropropane, CH₃CHClCH₃, by free radical substitution.

i) Write the overall equation and state the conditions for this reaction.

ii) Outline the mechanism by naming and providing relevant equations for each step in the formation of 2-chloropropane.

iii) Describe the limitations of this method of preparation.

A student named the alcohol molecule shown in Figure 1 as Z-1,4-dichlorohex-2-ene-6-ol.

Figure 1

State the errors the student has made in naming the molecule and give the correct IUPAC name.

Aspirin is an ester of salicylic acid, HOC₆H₄CO₂. Aspirin is formed when an ester bond is created between the salicylic acids OH group and ethanoic anhydride, (CH₃CO)₂O, in the presence of an acid catalyst, as shown in Figure 2. Ethanoic acid is also formed as a product.

Figure 2

i) Draw the skeletal formulae for both products of this reaction.

ii) Determine the molar mass of aspirin.

The organic compounds in Figure 3 below can be termed aliphatic, alicyclic or aromatic.

Figure 3 

Each response may contain more than one letter for the questions below.

i) Identify, using letters E, F, G, H, I, J, the compound(s) which are aliphatic.

ii) Identify, using letters E, F, G, H, I, J, the compound(s) which are alicyclic.

iii) Identify, using letters E, F, G, H, I, J, the compound(s) which are aromatic.

i) Using Figure 3 in part (c), state which compound E, F, G, H, I, J can be categorised as aliphatic but not alicyclic. Justify your answer.

ii) Describe a simple test that the student could carry out to confirm the presence of the functional group in compound H. Draw the structure of the organic product from the test.

Compounds with a carbon−carbon double bond are unsaturated. Figure 1 shows an unsaturated hydrocarbon.

Figure 1

i) Name the isomer shown in Figure 1.

ii) Justify the CIP naming rule for this isomer.

Two structural isomers of C₁₀H₁₈O are linalool and geraniol. They are unsaturated alcohols with similar chemical properties and are both used in perfumes.

The IUPAC names for both linalool and geraniol are shown in Table 1.

Table 1

Draw the skeletal formulae for these two isomeric alcohols.

The organic compounds below in Figure 2 are all made by living organisms.

Figure 2

i) State the IUPAC name for compound A.

ii) Compound D reacts readily with hydrogen chloride in an addition reaction. Two products are formed in this reaction, but one of the products is formed in much greater amounts than the other.

Draw the structures of both possible addition products of this reaction.

4.125 g of compound D (from part C) is reacted with an excess of hydrogen chloride. The mixture of products contains 95% by mass of one product and 5% by mass of the other product.

Calculate the mass of each product formed.