Shapes of Organic Molecules; σ & π Bonds (Cambridge (CIE) A Level Chemistry)

Explain how the concept of hybridisation can be used to explain the triple bond present in propyne.

Consider the molecule shown in Fig. 1.1 which contains both sigma and pi bonds.

 Fig. 1.1

 State the number of carbon atoms that exhibit sp² hybridisation in this molecule.

Complete Table 1.1 to show the hybridisation of the nitrogen atoms in NF₄⁺, N₂H₂ and N₂H₄. 

Table 1.1  

This question is about the structure and reactions of organic compounds.

Fig. 2.1 shows the displayed formula of a type of fuel known as gasoline. 

 Fig. 2.1

i) State the IUPAC name of gasoline. 

[1]

 ii) Give the general formula for the homologous series to which gasoline belongs. 

[1]

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

 i) State the type of organic mechanism used in this reaction. 

[1] 

ii) Draw the skeletal formula of the four monochlorinated isomers formed when the gasoline in Fig. 2.1 reacts with chlorine.  

[4] 

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

[1]

There are two possible reactions of 1-bromopropane with sodium hydroxide.

 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) Name compound X.  

[1]

 iii) In different reaction conditions, an alternative reaction occurs between the hydroxide ion and 1-bromompropane to form propene and a small molecule. 

State the reaction conditions and name the type of mechanism used in this alternative reaction. 

[2]

Pentanal reacts with hydrogen cyanide ions to form 2-hydroxyhexanenitrile as outlined in Fig. 2.3. 

 Fig. 2.3

 i) In terms of orbitals and bonding, explain why the shape of the carbonyl carbon highlighted in Fig. 2.3 can be described as trigonal planar. 

[3]

 ii) State the shape and bond angle adopted by the carbonyl carbon after the reaction with hydrogen cyanide. 

[1]

Hybridisation of the s and p orbitals can be used to explain the shapes observed in molecules.

Explain why cyclohexane C₆H₁₂ has a puckered, non-planar shape by making reference to the C–C–C bond angles and the type of hybridisation of carbon in the molecule. 

Urea, CO(NH₂)₂, is present in solution in animal urine. 

 Describe the hybridisation of C and N in the molecule, giving approximate bond angles.

Describe the hybridisation of the carbon atom in methane and explain how the concept of hybridisation can be used to explain the shape of the methane molecule.

A molecule of ethanol is shown in Fig. 3.1.

Fig. 3.1

Deduce the hybridisation of the carbon atom marked in the diagram below.

Ibuprofen is a common non-steroidal anti-inflammatory drug (NSAID). It contains a benzene ring and a carboxylic acid at the end of one of the branches as shown in Fig 1.1.

Fig 1.1

Deduce the number of sigma (σ) and pi (π) bonds in ibuprofen.

sigma .............................. 

pi ..............................

The ibuprofen molecule contains both sp² and sp³ hybridised carbon atoms.

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

Explain why the benzene ring is a planar hexagon.