Shapes of Organic Molecules; σ & π Bonds (Cambridge (CIE) AS Chemistry): Exam Questions

By reference to the hybridisation of the carbon atoms and orbital overlap, describe how the σ and π bonds are formed in the triple bond of propyne.

The structure of an organic molecule is shown in Fig. 1.1.

Fig. 1.1

State the number of carbon atoms that are sp² hybridised in this molecule.

Complete Table 1.1 to state the hybridisation of the nitrogen atom in each species.

Table 1.1

Gasoline is a mixture of hydrocarbons. Compound X is a component of gasoline. The displayed formula of compound X is shown in Fig. 2.1.

Fig. 2.1

i) State the systematic name of compound X.

[1]

ii) State the general formula for the homologous series to which compound X belongs.

[1]

Compound X shown in Fig. 2.1 can react with chlorine in the presence of UV light to form various chlorinated products.

i) Name the mechanism for this reaction.

[1]

ii) Draw the skeletal formulae of the four monochlorinated isomers formed when compound X reacts with chlorine.

[4]

iii) State the type of structural isomerism shown by the isomers in (ii).

[1]

Fig. 2.2 shows the mechanism for the reaction of aqueous sodium hydroxide with 1-bromopropane.

Fig. 2.2

i) State the role of the aqueous hydroxide ion in this reaction.

[1]

ii) State the systematic name of compound X.

[1]

iii) Under different reaction conditions, 1-bromopropane reacts with hydroxide ions to form propene.

State the conditions required for this reaction and name the mechanism.

[2]

Pentanal reacts with HCN in the presence of NaCN to form 2-hydroxyhexanenitrile as shown in Fig. 2.3.

Fig. 2.3

i) By reference to hybridisation and orbital overlap, explain why the carbonyl carbon in pentanal is trigonal planar.

[3]

ii) State the shape and bond angle around carbon-2 in 2-hydroxyhexanenitrile.

[1]

Explain why the ring of carbon atoms in cyclohexane, C₆H₁₂, is non-planar. In your answer, refer to the hybridisation of the carbon atoms and the C–C–C bond angles.

The structure of urea, CO(NH₂)₂, is shown in Fig. 3.1.

Fig. 3.1

Complete Table 3.1 to state the hybridisation and approximate bond angle around the carbon atom and each nitrogen atom in urea.

Table 3.1

State the hybridisation of the carbon atom in methane, CH₄. Name the shape of the molecule and explain why it has this shape.

hybridisation:

shape:

explanation:

A molecule of ethanol is shown in Fig. 3.2.

Fig. 3.2

State the hybridisation of the carbon atom marked in Fig. 3.2.

The structure of ibuprofen is shown in Fig. 1.1.

Fig. 1.1

State the number of pi (π) bonds and the number of chiral centres in a molecule of ibuprofen.

number of π bonds ..............................

number of chiral centres ..............................

State the number of sp² and sp³ hybridised carbon atoms in a molecule of ibuprofen.

sp² hybridised carbon atoms ..............................

sp³ hybridised carbon atoms ..............................

Describe and explain the shape of the benzene ring in ibuprofen.

In your answer, include:

• the bond angle between carbon atoms

• the hybridisation of the carbon atoms

• how orbital overlap forms σ and π bonds between the carbon atoms