Spectroscopy | OCR A-Level Chemistry A (H432)
Spectroscopy
- 88 questions
- 8 subtopics
- Module 6: Organic chemistry and analysis
- Component 02 and Component 03
Carbon-13 and proton NMR and what each feature of a spectrum tells you, and then the combination of elemental analysis, mass spectrometry, infrared and NMR that settles a structure..
It covers carbon-13 and proton NMR: peaks, chemical shift and integration, spin-spin splitting and predicting a spectrum, tMS, deuterated solvents and the D₂O shake, combining elemental analysis, mass spectrometry, IR and NMR, molecular formula from the molecular ion, and fragmentation losses, what IR and NMR each contribute to a structure, infrared absorption, global warming and breathalysers and a systematic approach and the degree of unsaturation.
Sample questions from Spectroscopy
Answer each one closed book first, then open the answer.
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Carbon-13 and proton NMR: peaks, chemical shift and integration
What does 'proton decoupled' mean in the context of carbon-13 NMR spectra?
Show the answer
Each carbon environment appears as a single peak rather than being split by coupling to attached protons. -
Spin-spin splitting and predicting a spectrum
A triplet splitting pattern indicates how many adjacent non-equivalent protons?
Show the answer
Two adjacent non-equivalent protons. -
TMS, deuterated solvents and the D₂O shake
Why do the protons and carbons in TMS appear at a chemical shift defined as zero?
Show the answer
Because they are in highly shielded environments, producing signals at higher field than most organic compounds. -
Combining elemental analysis, mass spectrometry, IR and NMR
What does NMR spectroscopy reveal about the structure of an organic compound?
Show the answer
NMR spectroscopy reveals the carbon and hydrogen environments within the molecule. -
Molecular formula from the molecular ion, and fragmentation losses
Once you know how many empirical formula units are in the molecular formula, how do you obtain the molecular formula?
Show the answer
Multiply the empirical formula by this whole number. -
What IR and NMR each contribute to a structure
What does the number of peaks or peak clusters in a ¹H NMR spectrum indicate?
Show the answer
The number of different hydrogen environments in the molecule. -
Infrared absorption, global warming and breathalysers
How do greenhouse gases keep the lower atmosphere warm?
Show the answer
The Earth's surface absorbs energy from the Sun and emits infrared radiation; the C=O, O–H and C–H bonds in CO₂, H₂O and CH₄ absorb this IR, vibrate more and re-emit the energy in all directions, some back towards the Earth, so less escapes to space. -
A systematic approach and the degree of unsaturation
What NMR features are used to deduce the detailed structure of a molecule?
Show the answer
Splitting patterns (to determine adjacent hydrogens) and integration (to determine the ratio of hydrogens in each environment).
The 8 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Carbon-13 and proton NMR: peaks, chemical shift and integration | Recall questions on what the number of peaks and the chemical shift indicate in each kind of NMR, what proton decoupling means, and what integration gives. | 10 |
| Spin-spin splitting and predicting a spectrum | Recall questions on the n + 1 rule, what a singlet, doublet, triplet and quartet each indicate, and predicting a spectrum from a structure. | 9 |
| TMS, deuterated solvents and the D₂O shake | Recall questions on tetramethylsilane as the NMR reference standard, deuterated solvents such as CDCl₃, and using a D₂O shake to identify O–H and N–H protons. | 10 |
| Combining elemental analysis, mass spectrometry, IR and NMR | Recall questions on what each technique contributes, why one alone is not enough, and how they are used together to separate possible isomers. | 11 |
| Molecular formula from the molecular ion, and fragmentation losses | Recall questions on scaling an empirical formula with the molecular ion peak, and on what losses of 15, 17, 29 and 45 mass units suggest. | 10 |
| What IR and NMR each contribute to a structure | Recall questions on identifying functional groups from infrared absorptions and the fingerprint region, and on what chemical shift, integration and splitting each add. | 15 |
| Infrared absorption, global warming and breathalysers | Recall questions on how covalent bonds absorb infrared radiation, greenhouse gases and the evidence linking carbon dioxide to global warming, and infrared monitoring of exhaust gases and breathalysers. | 12 |
| A systematic approach and the degree of unsaturation | Recall questions on the order in which the techniques are applied, calculating the degree of unsaturation, and why a carbon-13 spectrum may show fewer peaks than carbons. | 11 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby sections
OCR A-Level Chemistry A Active Recall Guide
Every section, not just this one. 1,913 questions with their answers.