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A bottle labelled ‘propanol’ contains one of two isomers of propanol - HSC - SSCE Chemistry - Question 27 - 2022 - Paper 1
Question 27
A bottle labelled ‘propanol’ contains one of two isomers of propanol. (a) Draw the TWO isomers of propanol. (b) Describe how \(^{13}C\) NMR spectroscopy might be u... show full transcript
Worked Solution & Example Answer:A bottle labelled ‘propanol’ contains one of two isomers of propanol - HSC - SSCE Chemistry - Question 27 - 2022 - Paper 1
Step 1
Draw the TWO isomers of propanol.
Answer
The two isomers of propanol are:
-
Propan-1-ol (n-propanol)
Structure:[ \text{CH}_3-\text{CH}_2-\text{CH}_2\text{OH} ]
- Propan-2-ol (isopropanol)
Structure:
[ \text{CH}_3-\text{C(OH)}-\text{CH}_3 ]
- Propan-2-ol (isopropanol)
These structures show the different arrangements of the hydroxyl (-OH) group.
Step 2
Describe how \(^{13}C\) NMR spectroscopy might be used to identify which isomer is in the bottle.
Answer
In (^{13}C) NMR spectroscopy, the number of signals represents the different environments of carbon atoms.
- Propan-1-ol will display two signals in the NMR spectrum due to its carbon atoms being in two distinct environments (the CH3 and CH2 groups).
- Propan-2-ol, on the other hand, shows three signals since the carbon atoms have unique environments (two CH3 groups and one CH).
Therefore, if the spectrum produced shows two signals, the isomer is propan-1-ol. If three signals are observed, it is propan-2-ol.
Step 3
Write equations to represent the oxidation reactions of the two isomers. Include reaction conditions.
Answer
-
Oxidation of Propan-1-ol:
[ \text{CH}_3-\text{CH}_2-\text{CH}_2\text{OH} + [O] \rightarrow \text{CH}_3-\text{CH}_2-\text{CHO} ]
Reaction conditions:
- Oxidising agent: ( H_2Cr_2O_7 ) or ( KMnO_4 )
- Mild conditions.
-
Oxidation of Propan-2-ol:
[ \text{CH}_3-\text{C(OH)}-\text{CH}_3 + [O] \rightarrow \text{CH}_3-\text{CO}-\text{CH}_3 ]
Reaction conditions:
- Oxidising agent: ( H^+/Cr_2O_7^{2-} ) or ( KMnO_4 )
- Mild heating.