The \({ }^{13}\text{C NMR}\) spectrum of an organic compound is shown below.
The organic compound could be
CHEMISTRY, M8 2023 HSC 36
An organic reaction pathway involving compounds \(\text{A, B,}\) and \(\text{C}\) is shown in the flow chart.
The molar mass of \(\text{A}\) is 84.156 g mol\(^{-1}\).
A chemist obtained some spectral data for the compounds as shown.
| \( \text{Data from} \ ^{1} \text{H NMR spectrum of compound C} \) | ||
| \( Chemical \ Shift \ \text{(ppm)} \) | \( Relative \ peak \ area \) | \( Splitting \ pattern \) |
| \(1.01\) | \(3\) | \(\text{Triplet}\) |
| \(1.05\) | \(3\) | \(\text{Triplet}\) |
| \(1.65\) | \(2\) | \(\text{Multiplet}\) |
| \(2.42\) | \(2\) | \(\text{Triplet}\) |
| \(2.46\) | \(2\) | \(\text{Quartet}\) |
| \( ^{1} \text{H NMR chemical shift data}\) | |
| \( Type \ of \ proton \) | \( \text{δ/ppm} \) |
| \( \ce{R - C\textbf{H}3,R - C\textbf{H}2 - R}\) | \(0.7-1.7\) |
| \( \left.\begin{array}{l}\ce{\textbf{H}3C - CO - \\-C\textbf{H}2 - CO -}\end{array}\right\} \begin{aligned} & \text { (aldehydes, ketones,} \\ &\text{carboxylic acids or esters) }\end{aligned}\) | \(2.0-2.6\) |
| \( \ce{R - C\textbf{H}O} \) | \(9.4-10.00\) |
| \( \ce{R - COO\textbf{H}} \) | \(9.0-13.0\) |
Identify the functional group present in each of compounds \(\text{A}\) to \(\text{C}\) and draw the structure of each compound. Justify your answer with reference to the information provided. (9 marks)
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Compound \(\text{A}\): Alkene
Compound \(\text{B}\): Secondary alcohol
Compound \(\text{C}\): Ketone
Reasoning as follows:
- Compound \(\text{A}\) is able to undergo an addition reaction to add water across a \(\ce{C=C}\) bond \(\Rightarrow \) Alkene
- Compound \(\text{B}\) is the product of the above hydration reaction and is therefore an alcohol.
- The \(\ce{^{13}C\ NMR}\) spectrum of Compound \(\text{A}\) confirms it is an alkene (132 ppm peak corresponding to the \(\ce{C=C}\) atoms). 3 spectrum peaks indicate 3 carbon environments. The molar mass of compound \(\text{A}\) is 84.156 g mol\(^{-1}\) which suggests symmetry within the molecule.
- The Infrared Spectrum of Compound \(\text{B}\) has a broad peak at approximately 3400 cm\(^{-1}\). This indicates the presence of an hydroxyl group and confirms \(\text{B}\) is an alcohol.
- Compound \(\text{C}\) is produced by the oxidation of Compound \(\text{B}\) with acidified potassium permanganate.
- Compound \(\text{C}\) is a carboxylic acid if \(\text{B}\) is a primary alcohol or a ketone if \(\text{B}\) is a secondary alcohol.
- Since the \(\ce{^{1}H NMR}\) spectrum of \(\text{C}\) does not show any peaks between 9.0 − 13.0 ppm, it cannot be a carboxylic acid. Compound \(\text{C}\) is therefore a ketone and Compound \(\text{B}\) is a secondary alcohol.
- The \(\ce{^{1}H NMR}\) spectrum shows 5 peaks \(\Rightarrow \) 5 hydrogen environments.
- Chemical shift and splitting patterns information indicate:
- 1.01 ppm – 1.05 ppm: \(\ce{CH3}\) (next to a \(\ce{CH2}\))
- 1.65 ppm: \(\ce{CH2}\) (with multiple neighbouring hydrogens)
- 2.42 ppm: \(\ce{CH2}\) (next to the ketone \(\ce{C=O}\) and a \(\ce{CH2}\))
- 2.46 ppm: \(\ce{CH2}\) (next to the ketone \(\ce{C=O}\) and a \(\ce{CH3}\))
Show Worked Solution
Compound \(\text{A}\): Alkene
Compound \(\text{B}\): Secondary alcohol
Compound \(\text{C}\): Ketone
Reasoning as follows:
- Compound \(\text{A}\) is able to undergo an addition reaction to add water across a \(\ce{C=C}\) bond \(\Rightarrow \) Alkene
- Compound \(\text{B}\) is the product of the above hydration reaction and is therefore an alcohol.
- The \(\ce{^{13}C\ NMR}\) spectrum of Compound \(\text{A}\) confirms it is an alkene (132 ppm peak corresponding to the \(\ce{C=C}\) atoms). 3 spectrum peaks indicate 3 carbon environments. The molar mass of compound \(\text{A}\) is 84.156 g mol\(^{-1}\) which suggests symmetry within the molecule.
- The Infrared Spectrum of Compound \(\text{B}\) has a broad peak at approximately 3400 cm\(^{-1}\). This indicates the presence of an hydroxyl group and confirms \(\text{B}\) is an alcohol.
- Compound \(\text{C}\) is produced by the oxidation of Compound \(\text{B}\) with acidified potassium permanganate.
- Compound \(\text{C}\) is a carboxylic acid if \(\text{B}\) is a primary alcohol or a ketone if \(\text{B}\) is a secondary alcohol.
- Since the \(\ce{^{1}H NMR}\) spectrum of \(\text{C}\) does not show any peaks between 9.0 − 13.0 ppm, it cannot be a carboxylic acid. Compound \(\text{C}\) is therefore a ketone and Compound \(\text{B}\) is a secondary alcohol.
- The \(\ce{^{1}H NMR}\) spectrum shows 5 peaks \(\Rightarrow \) 5 hydrogen environments.
- Chemical shift and splitting patterns information indicate:
- 1.01 ppm – 1.05 ppm: \(\ce{CH3}\) (next to a \(\ce{CH2}\))
- 1.65 ppm: \(\ce{CH2}\) (with multiple neighbouring hydrogens)
- 2.42 ppm: \(\ce{CH2}\) (next to the ketone \(\ce{C=O}\) and a \(\ce{CH2}\))
- 2.46 ppm: \(\ce{CH2}\) (next to the ketone \(\ce{C=O}\) and a \(\ce{CH3}\))
CHEMISTRY, M8 2021 HSC 21
Four organic liquids are used in an experiment. The four liquids are
-
- hexane
- hex-1-ene
- propan-1-ol
- propanoic acid
- State ONE safety concern associated with organic liquids and suggest ONE way to address this safety concern. (2 marks)
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- The organic liquids are held separately in four flasks but the flasks are not labelled. Tests were conducted to identify these liquids. The outcomes of the tests are summarised below. (2 marks)
Identify the FOUR liquids.
- What chemical test, other than those used in part (b), could be used to confirm the identification of ONE of the liquids? Include the expected observation in your answer. (2 marks)
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