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CBB042 Organic Chemistry - Reactions and Mechanisms

Title of Access to HE Diploma: Access to Pharmacy and Biomedical Sciences
Unit title(s): Organic Chemistry - Reactions and Mechanisms
Unit code(s): CBB042
Level 3

Scenario: You are a senior technician who has been asked to produce a PowerPoint on the synthesis of simple organic molecules, including mechanisms, creating questions and answers for trainee chemistry technicians. In your PowerPoint.

1. Explain the benzene reaction and mechanism of benzene compound showing the steps of reaction to produce a final traction by using curly arrows. AC (1.1)
2. Explain the differences between optical isomers and stereoisomerism using diagrams, to compare and contrast between them. AC (2.1, 2.2)

Complete the questions on the attached handout AC (1.1, 2.1, 2.2, 3.1, 3.2, 4.1)

Task 1 (AC 1.1)

1. Explain why benzene sp2 hybridized. Use diagram.
2. What types of bonding is present in benzene molecular? Use diagram
3. What is delocalized chemical bond in benzene? Use diagram

Task 2

Benzene reacts with chlorine in the presence of a halogen carrier, such as AlCl3. (AC 1.1)

1. 
   
   1. Write the equation for the reaction of benzene with chlorine.
   2. How does the halogen carrier allow the reaction to take place?
   3. Outline a mechanism for this reaction. Include curly arrows and relevant dipoles.
   4. State the name of this mechanism.
2. In contrast to benzene, the reaction of an alkene with bromine does not need a halogen carrier. Compare the different reactivities of benzene and alkenes towards chlorine.

Task 3

1. How optical isomers arise in organic molecules. Use diagram (AC 2.1)

2. 2-aminopropanoic acid (alanine) (AC 2.1)

   This is typical of naturally-occurring amino acids.

   

   Only one of these isomers occurs naturally: the (+) form. You cannot tell just by looking at the structures which this is. Select and explain which one is it, left or right and why?

3. Predict and explain the physical and chemical consequences of optical isomerism for the following structure: (AC 2.2)
   1. Explain what is optical isomerism?
   2. Explain what is Diastereomers and Enantiomers on the above diagram.
   3. Explain the physical and chemical properties of above diagrams.

Task 4.

Explain and construct different types of reaction mechanism in organic chemistry

(AC 3.1, 3.2)

1. Alkenes undergo electrophilic addition reactions to form saturated compounds.
   1. Define the term electrophile.
   2. The reaction between bromine and methylpropene is an electrophilic addition. Describe, with the aid of curly arrows, the mechanism for this reaction. Show the intermediate and the product along with any relevant dipoles and lone pairs of electrons.

2. Propanal, CH3CH2CHO, can be used in the synthesis of organic compounds.

   CH3CH2CHO reacts with NaBH4 in a nucleophilic addition reaction. The nucleophile can be represented as a hydride ion, H–. A mechanism for the reaction is shown below.

   
   1. Add 'curly arrows' to the mechanism to show how the intermediate reacts with the water molecule in step 2.
   2. Draw the structure of the organic product in the box above.
   3. What is meant by the term nucleophile?
3. Isomer L, C₅H₁₀, reacts with CI₂ in the presence of UV light to produce the organic product C₅H_gCI. The reaction takes place in three stages: initiation, propagation and termination.
   1. The reaction is initiated by the fission of CI₂. State the type of fission involved.
   2. Write an equation to illustrate the fission of CI₂ in (i).
   3. The fission of CI₂ leads to a chain reaction involving two propagation steps. Complete the equations for the two propagation steps.
      C₅H₁₀ ............ C₅H₉ .............
      C₅H₉ ............ ........ .............

Task 5

In the laboratory, ethanol can be oxidised with acidified potassium dichromate(VI). (AC 4.1)

1. The ethanol can be oxidised to form either ethanal, CH3CHO (Fig. 1), or ethanoic acid, CH3COOH (Fig. 2).

   The boiling points of ethanol, ethanal and ethanoic acid are given in the table below

   	CH3CH2OH	CH3CHO	CH3COOH
   boiling point / °C	8	21	118

   Use this table of boiling points to explain:

   1. why the organic product is likely to be ethanal if the apparatus shown in Fig. 1 is used,
   2. why the organic product is likely to be ethanoic acid if the apparatus shown in Fig. 2 is used.
2. Write a balanced equation for the oxidation of ethanol to ethanoic acid. Use [O] to represent the oxidising agent.
3. identifying a series of reactions to give a desired synthetic pathway:
   1. Starting from Alkane ending with Ester, stating the materials and conditions plus chemical equations.
4. To demonstrate an understanding of the characteristic tests which distinguish organic molecules, you will need to carry out a series of practical tests to identify the functional groups of unknown chemicals, followed by a full written report

Task 6

Explain with diagrams the selectivity and stereospecificity in organic reactions. (AC 4.1)