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QLDChemistryQuick questions

Unit 4: Structure, synthesis and design

Quick questions on Proton (1H) NMR spectroscopy (QCE Chemistry Unit 4)

6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is the molecular mass?
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| MS (M+) | | Are these functional groups present? | IR (O-H, C=O, N-H) | | How many hydrogen environments? Where?
What are counting hydrogen environments?
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Two hydrogens are in the same environment if they are equivalent by symmetry (interchangeable by a molecular symmetry operation or by free rotation of an attached methyl group). They give a single combined signal.
What is chemical shift?
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Each environment has a characteristic chemical shift range, determined by the inductive effects of attached groups. The QCAA syllabus uses the following reference ranges (the QCAA data booklet table for Unit 4 spectroscopy):
What is q1?
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Predict the number of 1H^1\text{H} NMR environments in (a) ethanol CH3CH2OH\text{CH}_3 \text{CH}_2 \text{OH}, (b) propan-2-ol. [2 marks]
What is q2?
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Predict the multiplicity (splitting) of each peak in propanal CH3CH2CHO\text{CH}_3 \text{CH}_2 \text{CHO} and give expected integration ratio. [4 marks]
What is q3?
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An unknown C3H8O\text{C}_3 \text{H}_8 \text{O} shows two singlets in 1H^1\text{H} NMR at 3.30ppm3.30 \, \text{ppm} (6 H) and 4.50ppm4.50 \, \text{ppm} (broad, 2 H). (a) Suggest a structure. (b) Identify the OH peak.

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