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CHEMISTRY, M8 2024 HSC 33

Acetone can be reduced, as shown.
 

  1. Identify the shape around the central carbon atom in each molecule.   (2 marks)

  2. Explain how spectroscopy could be used to monitor the progress of this reaction.  (3 marks)

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a.   Acetone:

→ Double bond and 2 single bonds coming off the central carbon atom    trigonal planar.

Product:

→ Contains single bonds coming off the central carbon atom (\Rightarrow\) tetrahedral. (Note: the hydrogen bonded to the central carbon atom in the product molecule is not shown due to the skeletal structure)
 

b.    Spectroscopy:

→ will differentiate between molecules with different carbon environments. This produces different signals on the spectrum.

→ The acetone would produce two signals on the spectrum. The first signal would be due to the groups either side of the central carbon between 20-50 ppm. The second signal would be from the carbonyl group between 190-220 ppm.

→ The product of the reduction would also produce two signals on the spectrum. The carbon with the hydroxyl group attached to it would produce a signal between 50-90 ppm and the groups either side would produce a signal between 5-40 ppm.

→ The reaction can be monitored by observing the disappearance of the carbonyl signal (190-220 ppm) and appearance of the hydroxyl signal (50-90 ppm) as acetone is reduced to the product.

Show Worked Solution

a.   Acetone:

→ Double bond and 2 single bonds coming off the central carbon atom trigonal planar.

Product:

→ Contains single bonds coming off the central carbon atom    tetrahedral. (Note: the hydrogen bonded to the central carbon atom in the product molecule is not shown due to the skeletal structure)

♦ Mean mark (a) 44%.

  

b.    Spectroscopy:

→ will differentiate between molecules with different carbon environments. This produces different signals on the spectrum.

→ The acetone would produce two signals on the spectrum. The first signal would be due to the groups either side of the central carbon between 20-50 ppm. The second signal would be from the carbonyl group between 190-220 ppm.

→ The product of the reduction would also produce two signals on the spectrum. The carbon with the hydroxyl group attached to it would produce a signal between 50-90 ppm and the groups either side would produce a signal between 5-40 ppm.

→ The reaction can be monitored by observing the disappearance of the carbonyl signal (190-220 ppm) and appearance of the hydroxyl signal (50-90 ppm) as acetone is reduced to the product.

CHEMISTRY, M8 2022 VCE 28 MC

The spectrum of an organic compound is shown below.

The organic compound could be

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→ The has five peaks indicating 5 different carbon environments within the molecule.

→ The peak at 140 indicates the presence of the .

♦ Mean mark 42%.
COMMENT: Solving by elimination is an effective strategy here.

CHEMISTRY, M8 2023 HSC 36

An organic reaction pathway involving compounds and is shown in the flow chart.
 

The molar mass of is 84.156 g mol.

A chemist obtained some spectral data for the compounds as shown.
 

 
 δ
 
 

Identify the functional group present in each of compounds to and draw the structure of each compound. Justify your answer with reference to the information provided.  (9 marks) 

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Compound : Alkene
 

Compound : Secondary alcohol
 

Compound : Ketone
 

Reasoning as follows:

→ Compound is able to undergo an addition reaction to add water across a bond    Alkene

→ Compound is the product of the above hydration reaction and is therefore an alcohol.

→ The spectrum of Compound confirms it is an alkene (132 ppm peak corresponding to the atoms). 3 spectrum peaks indicate 3 carbon environments. The molar mass of compound is 84.156 g mol which suggests symmetry within the molecule.

→ The Infrared Spectrum of Compound has a broad peak at approximately 3400 cm. This indicates the presence of an hydroxyl group and confirms is an alcohol.

→ Compound is produced by the oxidation of Compound with acidified potassium permanganate.

→ Compound is a carboxylic acid if is a primary alcohol or a ketone if is a secondary alcohol.

→ Since the spectrum of does not show any peaks between 9.0 − 13.0 ppm, it cannot be a carboxylic acid. Compound is therefore a ketone and Compound is a secondary alcohol.

→ The spectrum shows 5 peaks 5 hydrogen environments.

→ Chemical shift and splitting patterns information indicate:

1.01 ppm – 1.05 ppm: (next to a )

1.65 ppm: (with multiple neighbouring hydrogens)

2.42 ppm: (next to the ketone and a )

2.46 ppm: (next to the ketone and a )

Show Worked Solution

Compound : Alkene
 

Compound : Secondary alcohol
 

Compound : Ketone
 

Reasoning as follows:

→ Compound is able to undergo an addition reaction to add water across a bond    Alkene

→ Compound is the product of the above hydration reaction and is therefore an alcohol.

→ The spectrum of Compound confirms it is an alkene (132 ppm peak corresponding to the atoms). 3 spectrum peaks indicate 3 carbon environments. The molar mass of compound is 84.156 g mol which suggests symmetry within the molecule.

→ The Infrared Spectrum of Compound has a broad peak at approximately 3400 cm. This indicates the presence of an hydroxyl group and confirms is an alcohol.

→ Compound is produced by the oxidation of Compound with acidified potassium permanganate.

→ Compound is a carboxylic acid if is a primary alcohol or a ketone if is a secondary alcohol.

→ Since the spectrum of does not show any peaks between 9.0 − 13.0 ppm, it cannot be a carboxylic acid. Compound is therefore a ketone and Compound is a secondary alcohol.

→ The spectrum shows 5 peaks 5 hydrogen environments.

→ Chemical shift and splitting patterns information indicate:

1.01 ppm – 1.05 ppm: (next to a )

1.65 ppm: (with multiple neighbouring hydrogens)

2.42 ppm: (next to the ketone and a )

2.46 ppm: (next to the ketone and a )

CHEMISTRY, M8 2019 HSC 19 MC

Compound shows three signals in its spectrum.

Treatment of with hot acidified potassium permanganate produces a compound . Compound turns blue litmus red.

Compound produces compound upon reaction with hot concentrated sulfuric acid.

Which of the following correctly identifies compounds , and ?
 

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→ The given information suggests that compound is a carboxylic acid because it is produced through the oxidation of compound , a primary alcohol, with an oxidising agent and turns blue litmus red.

→ The treatment of compound with hot concentrated sulfuric acid results in a dehydration reaction.

→ In summary, the information provided suggests that compound is a carboxylic acid and compound is a primary alcohol, and that the treatment of compound with hot concentrated sulfuric acid results in a dehydration reaction.


♦♦♦ Mean mark 33%.

CHEMISTRY, M8 2022 HSC 27

A bottle labelled 'propanol' contains one of two isomers of propanol.

  1. Draw the TWO isomers of propanol.   (2 marks)
     

  1. Describe how spectroscopy might be used to identify which isomer is in the bottle.   (2 marks)
  1. Each isomer produces a different product when oxidised.
  2. Write equations to represent the oxidation reactions of the two isomers. Include reaction conditions.   (3 marks)
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a.    Isomer 1:

Isomer 2:

b.   Identifying isomers with spectroscopy:

→ this can be used to identify the isomers in the bottle because they show a different number of signals which helps deduce the carbon environment.

→ Propan-1-ol contains 3 environments so it would have 3 peaks on a spectrum whereas propan-2-ol only contains 2 environments (due to symmetry), so it would only have 2 signals on a spectrum.

c.  


  

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a.    Isomer 1:

   

Isomer 2:

   

b.   Identifying isomers with spectroscopy:

→ this can be used to identify the isomers in the bottle because they show a different number of signals which helps deduce the carbon environment.

→ Propan-1-ol contains 3 environments so it would have 3 peaks on a spectrum whereas propan-2-ol only contains 2 environments (due to symmetry), so it would only have 2 signals on a spectrum.

c.  


  


♦ Mean mark (c) 52%.

CHEMISTRY, M8 2022 HSC 12 MC

Which isomer of would have the fewest signals in ?
 

 

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→ Structure D only contains two unique carbon environments, and thus would only contain two signals on a spectrum.

→ Structure A contains 3 signals, structure B contains 5 signals, and structure C contains 4 signals.


♦ Mean mark 49%.