Optical isomerism

How many stereoisomers does the compound CH₃CH(Br)CH=CHCH(Cl)CH₃ have?

A 2

B 4

C 6

D 8

This question is about different areas of chemistry.

Why do all average bond enthalpies have a positive value?

Determine the C–H bond enthalpy, in kJ mol^–1, using the information above.

C–H bond enthalpy =........ kJ mol^–1

Hydrogen gas is being considered as a household fuel to replace methane.

The enthalpy change of formation, _fH, for H₂O(l) is –285.8 kJ mol^–1.

Determine the energy released when 60.0 m³ of hydrogen is used as a household fuel at RTP.

Give your answer to 3 significant figures and in standard form.

Compound A is a chloride of a Period 3 element.

A student carries out the 2 steps below to find the formula of compound A.

Step 1 The student adds 5.00 10^–4 mol of compound A to water. A colourless solution is formed.

Step 2 The colourless solution reacts with exactly 60.0 cm³ of 2.50 10^–2 mol dm^–3 AgNO₃(aq) to form a white precipitate.

Write an ionic equation, with state symbols, for the reaction in Step 2.

Determine the formula of compound A.

Compound B, shown below, is an antiviral medicine.

What is the molecular formula of compound B ?

How many chiral carbon atoms are there in one molecule of compound B ?

This question is about -amino acids.

The general formula of an -amino acid is RCH(NH₂)COOH.

Most -amino acids show optical isomerism.

Explain the term optical isomerism.

The -amino acid valine has the R group of –CH(CH₃)₂.

What is the systematic name of valine?

Draw diagrams to show 3D structures of the optical isomers of valine.

How many optical isomers are possible for compound E ?

A student hydrolyses compound E with dilute hydrochloric acid, HC l (aq).

Draw the structures of the organic products formed by this hydrolysis.

The structure of a drug is shown below:

How many chiral carbon atoms are there in a molecule of the drug?

A 5

B 6

C 7

D 8

This question is about unsaturated hydrocarbons.

What is the systematic name of hydrocarbon A ?

Compounds B and C are branched hydrocarbons that are structural isomers of C₆H₁₂.

Compounds B and C both have stereoisomers.

• Compound B has cis and trans isomers but does not have optical isomers.

• Compound C has optical isomers but does not have cis and trans isomers.

What is meant by the term structural isomers ?

What is meant by the term stereoisomers ?

Draw structures for the cis and trans isomers of the branched hydrocarbon B.

Draw 3D structures for the optical isomers of compound C.

Compounds D and E are two more structural isomers of C₆H₁₂.

Compounds D and E do not show stereoisomerism.

Table 16.1 shows NMR and infrared (IR) spectral data for D and E.

Draw the structures of D and E and explain how the spectral data in Table 16.1 provides evidence for the structures.

Draw the structures of the products you would expect from the ozonolysis of the two compounds below.

A student carries out an investigation on vitamin C, C₆H₈O₆.

Vitamin C is extremely soluble in water. This means that vitamin C is removed rapidly from the body. ‘Vitamin C ester’ is available in tablet form as a less soluble source of vitamin C which stays in the body for longer.

Suggest why vitamin C is extremely soluble in water.

A ‘vitamin C ester’ tablet contains an ester with the molecular formula C₂₂H₃₈O₇.

This ester can be prepared by reacting vitamin C with a long chain carboxylic acid, C_xH_yCOOH, in the presence of an acid catalyst.

Vitamin C and the long chain carboxylic acid react in a 1:1 molar ratio.

Determine x and y in the formula of this carboxylic acid.

Vitamin C, C₆H₈O₆, is a weak acid (K_a = 7.94 x 10^–5 (mol dm^–3)), which is often referred to as ascorbic acid.

The label on a carton of orange juice lists the mass of vitamin C, in mg, in a typical serving of 150 cm³.

The student carries out an investigation to check the vitamin C content in the orange juice.

Vitamin C can be oxidised by iodine:

The student dilutes 150 cm³ of the orange juice with water to 250.0 cm³ in a volumetric flask.

The student then titrates 25.0 cm³ volume of this solution with 9.60 × 10^–4 mol dm^–3 iodine solution, I₂(aq).

The mean titre of I₂(aq) is 22.50 cm³.

Determine the mass, in mg, of vitamin C in a 150 cm³ serving of the orange juice.

Which type(s) of stereoisomerism is/are shown by 2,4-dimethylhex-2-ene?

A E / Z isomerism only.

B Optical isomerism only.

C Both E / Z isomerism and optical isomerism.

D Neither E / Z isomerism nor optical isomerism.

This question is about organic acids.

Table 18.1 shows the R groups in four amino acids.

Most amino acids show optical isomerism.

Explain the term optical isomerism.

Draw 3-D diagrams to show the optical isomers of alanine.

How many optical isomers does threonine have?

Ibuprofen, shown below, is used as a painkiller.

What is the molecular formula of ibuprofen?

One ibuprofen tablet contains 400 mg of ibuprofen.

Calculate the number of ibuprofen molecules in one ibuprofen tablet.

Give your answer to 3 significant figures.

Tablets based on ibuprofen and lysine are now available from pharmacies.

These tablets are claimed to act faster than ibuprofen by being absorbed into the body more quickly than ibuprofen alone.

One type of these tablets contains a salt of ibuprofen and the amino acid lysine (R = –(CH₂)₄NH₂) in a 1:1 molar proportion.

Suggest why tablets based on a salt of ibuprofen should act faster in the body than ibuprofen.

Hydrocarbon A can be reacted with bromine in the presence of ultraviolet radiation to prepare (CH₃)₃CCHBrCH₃.

What is the systematic name for (CH₃)₃CCHBrCH₃?

(CH₃)₃CCHBrCH₃has stereoisomers.

Explain the term stereoisomers and name this type of stereoisomerism.

Explanation:........

Type of stereoisomerism:........

Draw 3D diagrams for the stereoisomers of (CH₃)₃CCHBrCH₃.

Complete the table to show the mechanism for the reaction of hydrocarbon A with Br₂ to form (CH₃)₃CCHBrCH₃.

Use skeletal formulae for all organic compounds. Use ‘dots’ (●) to show the position of unpaired electrons.

State two limitations of using radical substitution in organic synthesis.

What is the number of chiral carbon atoms in the steroid molecule below?

This question is about unsaturated aldehydes and alcohols.

Outline the reaction mechanism for the formation of one of the organic products.

Include curly arrows and relevant dipoles.

Explain why one of the organic products forms in a much greater quantity than the other organic product.

Describe how the observations from a chemical test would distinguish between geraniol and citronellal.

What is the molecular formula of geraniol?

Explain why geraniol and citronellal are structural isomers of each other.

Explain the term stereoisomerism.

Dettol ® is a disinfectant containing the antiseptic chloroxylenol, shown below.

Chloroxylenol is a weak Brønsted–Lowry acid.

What is the systematic name of chloroxylenol?

Predict the number of peaks in a¹³C NMR spectrum of chloroxylenol.

Name the functional group responsible for the acidity of chloroxylenol and describe a simple test which would confirm the presence of this group.

Functional group........

Test........

A student measures the pH of the contents in a bottle of Dettol ® as 5.14.

The label on the bottle shows the percentage of chloroxylenol in Dettol ® as 4.80% i.e. 100 cm³ of Dettol^® contains 4.80 g of chloroxylenol.

Assume the following:

• Chloroxylenol is the only acidic component in Dettol ®.

• Chloroxylenol is a weak monobasic acid.

• The density of Dettol ® is 1.00 g cm −3.

Write the equation, using molecular formulae, for the acid dissociation of chloroxylenol.

Calculate the acid dissociation constant, K_a, for chloroxylenol.

K_a =........ mol dm⁻³

Dettol^® contains other chemicals including -terpineol, shown below.

-Terpineol is a chiral compound.

Show with an asterisk, (*), the chiral centre(s) in the structure of -terpineol.

-Terpineol meets the requirements for E / Z isomerism. However, only one E / Z isomer of -terpineol exists.

Explain

• why -terpineol meets the requirements for E / Z isomerism

• whether -terpineol is an E- or Z- isomer

• why only one E / Z isomer of -terpineol exists.

-Terpineol contains two functional groups.

For each functional group, choose a reagent that reacts with that group only. Draw the structures for the organic products of the reactions.

Show structures for organic compounds.

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

Reagent(s)........

Name of functional group that reacts........

Structure of organic product

How many straight-chain structural isomers of C₇H₁₅Cl contain a chiral carbon atom?

A 1

B 2

C 3

D 4

The general formula of an -amino acid is RCH(NH₂)COOH.

The -amino acid cysteine (R = CH₂SH) shows optical isomerism.

Draw 3-D diagrams to show the optical isomers of cysteine.

The -amino acid lysine (R = (CH₂)₄NH₂) reacts with an excess of dilute hydrochloric acid to form a salt.

Draw the structure of the salt formed in this reaction.

-Amino acids can react to form proteins.

A short section of a protein chain is shown below.

A student hydrolyses the protein with hot NaOH(aq).

Draw the structures of the organic products formed from this section of the protein.

This question is about the hydrolysis of haloalkanes.

The rate of hydrolysis of a haloalkane depends on the halogen present.

State and explain how the halogen in the haloalkane affects the rate of hydrolysis.

A student hydrolyses a haloalkane, E, using the following method.

• 0.0100 mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture containing an organic product F.

• The reaction mixture is neutralised with dilute nitric acid.

• Excess AgNO₃(aq) is added to the reaction mixture. 1.88 g of a precipitate G forms.

Organic product, F, has a molar mass of 74.0 g mol⁻¹ and has a chiral carbon atom.

Draw a labelled diagram to show how the student would carry out the hydrolysis of haloalkane E.

Analyse the information to identify E, F and G.

Show your working.

What is the number of chiral centres in the molecule below?