Organic Chemistry 1 · Molecular evidence and structure
Proton NMR reasoning: practice problems
32 problems, each with its worked solution. Open one to read every step, or filter by tag.
Predict the product 4
- Predict a methine patternApply first-order splitting to a methine with six equivalent methyl neighbors.
- Splitting of the Middle CH2 in 1-ChloropropaneApply the n + 1 rule to a CH2 flanked by a CH3 and a CH2 with similar coupling constants.
- Predict the 1H NMR Spectrum of 2-ButanoneMatch a ketone to its signal list using shift, integration and splitting together.
- Find the compound with a septetUse the n+1 rule to pick the structure giving a septet and a doublet.
Classify 5
- Count nonexchangeable environmentsUse symmetry and exchange assumptions to count proton sets.
- Spot diastereotopic protonsIdentify CH2 protons that are diastereotopic because of a nearby stereocentre.
- Classify the CH2 Hydrogens of EthanolClassify the methylene hydrogens of ethanol with the substitution test and predict whether they give one signal.
- Which Dichlorobenzene Gives Three Aromatic SignalsCount the aromatic proton environments of the three dichlorobenzene isomers from ring symmetry.
- Assign a chemical shift regionMatch a proton type to its typical 1H chemical shift region.
Compare 2
- Compare methylene hydrogensApply the replacement test in a molecule containing a fixed stereocenter.
- Rank Methyl Halide 1H Shifts: CH3F to CH3IRank the methyl signals of the four methyl halides by chemical shift from halogen electronegativity.
Calculate 8
- Turn integrals into proton countsNormalize a relative integral scale using a known hydrogen total.
- Compare two magnet strengthsSeparate field-independent ppm shifts from frequency differences in hertz.
- Convert δ 3.40 to Hz on a 400 MHz SpectrometerConvert a chemical shift in ppm to a frequency offset from TMS in hertz at a given field strength.
- Protons from integrationConvert relative integrals into a proton count using the molecular formula.
- Convert a coupling to ppmConvert a separation in hertz to ppm at a given spectrometer frequency.
- Mole Ratio of Benzene and Cyclohexane by 1H NMRFind the mole ratio of two compounds in a mixture by normalizing each integral to its number of protons.
- Count 1H Signals in 2-Methyl-2-buteneCount the proton environments of a trisubstituted alkene whose geminal methyls sit cis and trans to a vinyl H.
- Count 1H NMR signalsCount chemically distinct proton environments using symmetry.
Find the error 2
- Diagnose a disappearing resonanceInterpret D₂O exchange without treating it as a carbon-skeleton change.
- Why the OCH3 of MTBE Is a Singlet, Not a DoubletFind which neighbors can split a signal when the adjacent atoms of an ether carry no hydrogens.
Interpret the evidence 5
- Interpret a downfield quartetRecognize coupling to an aldehydic proton in a simple first-order model.
- Read a para-substituted ring patternInterpret two aromatic doublets of 2H each as a para-disubstituted ring.
- E or Z Cinnamic Acid From the Vinyl J ValueAssign the double-bond geometry of a 1,2-disubstituted alkene from its vicinal vinyl coupling constant.
- Identify the C8H10 Arene With Two SingletsPick the C8H10 aromatic isomer whose symmetry makes all ring hydrogens and both methyls equivalent.
- Structure from 1H dataChoose the structure that fits a full 1H NMR data set for C4H8O2.
Work backward 2
- Recover a fragment from paired signalsInfer a coupled ethyl fragment without overclaiming molecular identity.
- Methyl Propanoate or Ethyl Acetate From 1H DataWork back from which side of the ester oxygen carries the singlet and the ethyl group to name the isomer.
Plan a synthesis 2
- Plan a mixture calculationNormalize distinct molecular signal sizes before calculating a mixture ratio.
- Tell 1-Propanol From 2-Propanol by 1H NMRPlan which 1H signal separates two constitutional isomers of an alcohol most reliably.
Explain why 2
- Predict splitting from two coupling constantsDistinguish independent coupling constants from equivalent-neighbor splitting.
- Why 1-Hexyne Is Upfield of 1-Hexene: AnisotropyExplain the upfield acetylenic C–H shift with the induced field of the circulating triple-bond π electrons.
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