Optical isomerism

This question is about isomerism.

Compound L has this structure.

Use IUPAC rules to name L.

Explain why L exists as stereoisomers.

Compound M has the same carbon chain as L but the double bond is in a different position.

M also exists as stereoisomers.

Draw the structural formula of M.

Explain why M exists as stereoisomers.

Structural formula

Figure 1 shows part of the mechanism when L reacts with hydrogen bromide.

Complete Figure 1 to show the next step in the mechanism that gives the

Compounds V, W, X and Y are isomers with the molecular formula C₅H₁₀O₂

Isomers V and W are carboxylic acids with formulas that can be written as C₄H₉COOH

Give an equation for the reaction of C₄H₉COOH with sodium hydrogencarbonate.

Isomer V has an asymmetric carbon atom.

Deduce the structure of V.

Isomer W has four peaks in its¹H NMR spectrum.

Deduce the structure of W.

Deduce the integration ratio for the four peaks in the¹H NMR spectrum of W.

Integration ratio

Table 2 shows information about the peaks in the¹H NMR spectrum of isomer Y.

Draw the parts of the structure of Y that can be deduced from each of these peaks.

Deduce the structure of Y.

State how many peaks are in the¹³C NMR spectrum of Y.

Part of structure from peak at δ = 3.65 ppm

Part of structure from peak at δ = 1.19 ppm

Acrylonitrile, H₂C=CHCN, can be used as a starting material for the synthesis of butane-1,4-diamine, as shown in this reaction scheme.

Use IUPAC rules to name isomer W.

Reaction 1 produces a mixture of W and two other isomers.

Draw the structures of the two other isomers.

Explain, by considering the mechanism of this reaction, why all three isomers are formed.

The reaction scheme is repeated here.

Identify the reagent that is warmed with isomer W in reaction 2.

State the other reaction condition needed.

State the reagent and reaction conditions needed for reaction 3.

Give an equation for reaction 3.

Reagent and conditions

Equation

An incomplete equation for the formation of nylon 4,6 from five molecules of butane-1,4-diamine and five molecules of hexanedioic acid is shown.

Deduce the values of x and y in this equation.

Figure 6 shows a section of the nylon 4,6 polymer molecule.

Figure 6

Draw, on Figure 6, another section of nylon 4,6 polymer showing two hydrogen bonds between the two sections.

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.

Mechanism to form alkenes

Mechanism to form alcohols

Define the term stereoisomers.

Deduce the name of isomer A.

Explain why A does not exhibit stereoisomerism.

Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.

Deduce the name of isomer B and the name of isomer C.

Explain the origin of the stereoisomerism in B and C.

Draw 3D representations of enantiomers D and E to show how their structures are related.

A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The suggested method is:

• add equal volumes of the three halogenoalkanes to separate test tubes

• add equal volumes of aqueous silver nitrate to each test tube

• record the time taken for a precipitate to appear in each test tube.

State and explain the order in which precipitates appear.

Order in which precipitates appear

This question is about isomers with the molecular formula C₅H₁₀O

Draw the skeletal formula of a branched chain aldehyde with molecular formula C₅H₁₀O that is optically active.

Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C₅H₁₀O

Draw the E and Z forms of a structural isomer of C₅H₁₀O that shows both optical and geometric isomerism.

Isomer J is cyclic and has an ether functional group (C–O–C) Isomer J has only three peaks in its¹³C NMR spectrum.

Draw two other cyclic isomers of C₅H₁₀O that have an ether functional group and only three peaks in their¹³C NMR spectra.

Which statement about (CH₃)₂CHCH₂COOH is correct?

Prilocaine is used as an anaesthetic in dentistry. Figure 3 shows the structure of prilocaine.

Draw a circle around any chiral centre(s) in Figure 3.

Identify the functional group(s) in the prilocaine molecule.

Tick (✓) the box(es) corresponding to the functional group(s).

Prilocaine is completely hydrolysed in the human body to give a mixture of products.

Draw the structures of the two organic products formed in the complete hydrolysis of prilocaine in acidic conditions.

Figure 4 shows optical isomers F and G.

Isomer F is the active compound in the medicine ibuprofen.

In the manufacture of ibuprofen both isomers F and G are formed. An enzyme is then used to bind to isomer G and catalyse its hydrolysis.

After the products of hydrolysis of G are removed, a pure sample of isomer F is collected.

Explain how a structural feature of this enzyme enables it to catalyse the hydrolysis of isomer G but not the hydrolysis of isomer F.

Which does not contain an asymmetric carbon atom?

This question is about amines.

Give an equation for the preparation of 1,6-diaminohexane by the reaction of 1,6-dibromohexane with an excess of ammonia.

Complete the mechanism for the reaction of ammonia with 6-bromohexylamine to form 1,6-diaminohexane.

Suggest the structure of a cyclic secondary amine that can be formed as a by-product in this reaction.

Mechanism

Cyclic secondary amine

1,6-Diaminohexane can also be formed in a two-stage synthesis starting from 1,4-dibromobutane. Suggest the reagent and a condition for each stage in this alternative synthesis.

Stage 1 reagent and condition

Stage 2 reagent and condition

Explain why 3-aminopentane is a stronger base than ammonia.

Justify the statement that there are no chiral centres in 3-aminopentane.

Ethanal reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile.

Name the mechanism for the reaction between potassium cyanide and ethanal.

The 2-hydroxypropanenitrile formed by the reaction in question 04.1 is a mixture of equal amounts of two isomers.

State the name of this type of mixture.

Explain how the structure of ethanal leads to the formation of two isomers.

Draw 3D representations of the two isomers to show the relationship between them.

3D representations

2-Hydroxypropanenitrile can be used in the synthesis of the monomer,

Suggest a suitable reagent and conditions for the conversion of 2-hydroxypropanenitrile into acrylonitrile.

Draw a section of the polymer polyacrylonitrile, showing three repeating units.

Give the IUPAC name of CH₃CH₂CH₂CH₂CH(OH)CN

Describe how you would distinguish between separate samples of the two

Explain why the reaction produces a racemic mixture.

An isomer of CH₃CH₂CH₂CH₂CHO reacts with KCN followed by dilute acid to form a compound that does not show stereoisomerism.

Draw the structure of the compound formed and justify why it does not show stereoisomerism.

Structure

Justification