Question

The infrared spectrum of compound \(\mathrm{A}_{1} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}\), shows a strong, sharp peak at \(1724 \mathrm{~cm}^{-1}\). From this information and its \({ }^{1} \mathrm{H}\)-NMR spectrum, deduce the structure of compound A.

Short answer

Question: Given a molecular formula C6H12O and an infrared spectrum with a peak at 1724 cm-1, describe the expected 1H-NMR features for the possible structures of the compound. Answer: With the given molecular formula and the IR peak at 1724 cm-1, the possible structures of the compound are 2-hexanone, 3-hexanone, and hexanal. The expected 1H-NMR features for each structure are: 1. 2-hexanone: a. A singlet for the 3 protons of the CH3 group next to the carbonyl group. b. A singlet or multiplet for the 2 protons of the CH2 group attached to the carbonyl group. c. Two multiplets for the other CH2 groups in the chain. 2. 3-hexanone: a. A singlet or multiplet for the 2 protons of the CH2 group next to the carbonyl group. b. Two singlets or multiplets for the other CH2 groups. 3. Hexanal: a. A singlet for the 3 protons of the CH3 group at the end of the chain. b. A singlet or multiplet for the 2 protons of the CHO group. c. Several singlets or multiplets for the other CH2 groups in the chain.

Step-by-step solution

Analyze the infrared spectrum

The IR spectrum displays a strong, sharp peak at 1724 cm-1. This peak is characteristic for the carbonyl group (C=O), which can be present in different functional groups like aldehydes, ketones, carboxylic acids, and so on. Considering the molecular formula of A (C6H12O), the carbonyl group being present in the compound leads us to believe that it might be an aldehyde or ketone.

List possible structures consistent with molecular formula

1. Possible structures for a ketone: a. 2-hexanone: CH3COCH2CH2CH2CH3 b. 3-hexanone: CH3CH2COCH2CH2CH3 2. Possible structure for an aldehyde: a. Hexanal: CH3CH2CH2CH2CH2CHO We can't choose the correct structure without analyzing the 1H-NMR spectrum. Since the 1H-NMR data is not given in the exercise, we can only describe what features we would expect in the NMR spectrum for each possible structure.

Describe expected 1H-NMR features for each possible structure

1. 2-hexanone: a. A singlet corresponding to the 3 protons of the CH3 next to the carbonyl group. b. A singlet or multiplet corresponding to the 2 protons of the CH2 attached to the carbonyl group. c. Two multiplets for the other CH2 groups in the chain. 2. 3-hexanone: a. A singlet or multiplet corresponding to the 2 protons of the CH2 next to the carbonyl group. b. Two singlets or multiplets for the other CH2 groups. 3. Hexanal: a. A singlet corresponding to the 3 protons of the CH3 group at the end of the chain. b. A singlet or multiplet corresponding to the 2 protons of the CHO group. c. Several singlets or multiplets for the other CH2 groups in the chain. By analyzing an actual 1H-NMR spectrum, we could identify the structure of the compound A by matching the expected features with the observed peaks.