Organic Chemistry 1 · Molecular evidence and structure
Integrating structure evidence: practice problems
28 problems, each with its worked solution. Open one to read every step, or filter by tag.
Predict the product 2
- C₈H₁₀ with three carbon signalsUse ¹³C signal counts to choose among C₈H₁₀ aromatic isomers.
- Predict the IR and NMR data of diethyl etherPredict the IR, ¹H and ¹³C NMR data of diethyl ether and reject data of its C₄H₁₀O isomers.
Classify 2
- Resolve two oxygen connectivitiesCombine exchange, IR and proton environment count.
- C₃H₆O with O–H and C=C bands: classify the groupsCombine formula, IR and ¹H NMR evidence to name the functional groups of C₃H₆O (allyl alcohol).
Compare 5
- Test a displayed ester hypothesisCheck an explicit candidate against integral, splitting and formula evidence.
- C₃H₆O₂ ester: ethyl formate or methyl acetate?Compare C₃H₆O₂ ester and acid isomers using ¹H chemical shifts and splitting (ethyl formate).
- C₄H₈ isomers: 2-methylpropene, but-2-ene or cyclobutane?Use ¹H splitting and ¹³C signal counts to choose among C₄H₈ alkene and ring isomers (2-methylpropene).
- C₄H₈O after a D₂O shakeUse D₂O exchange to separate an alcohol from an ether isomer.
- C₅H₈: alkyne or diene?Use IR to decide between a terminal alkyne and a diene of formula C₅H₈.
Calculate 3
- Reconcile an unsaturation budgetAllocate DBE among a benzene ring and a carbonyl without adding an extra ring.
- C₅H₈O ketone: how many rings? (cyclopentanone)Split a C₅H₈O unsaturation budget between a carbonyl and rings using IR and NMR evidence.
- C₈H₉NO amide: count the degrees of unsaturationCalculate degrees of unsaturation for a nitrogen-containing formula and assign them to an aromatic amide (acetanilide).
Find the error 3
- Diagnose a candidate contradictionReject a drawn ketone when aldehyde evidence requires another connectivity.
- Audit a displayed atom budgetReject a plausible functional group when its carbon count contradicts formula.
- C₄H₁₀O drawn as butan-2-ol but no O–H bandFind the decisive contradiction between C₄H₁₀O data and a proposed butan-2-ol structure.
Interpret the evidence 5
- Select a small carbonyl structureCombine formula, equivalent proton count and carbonyl evidence.
- C₄H₈O₂ acid: 2-methylpropanoic or butanoic acid?Assemble a C₄H₈O₂ carboxylic acid from IR, ¹H splitting and ¹³C signal counts (2-methylpropanoic acid).
- C₄H₉Cl with one signalIdentify a C₄H₉Cl isomer from a single ¹H NMR signal.
- C₆H₁₂O₂ ester with a 9H singletAssemble a C₆H₁₂O₂ ester from IR and ¹H NMR fragments.
- C₉H₁₀O₂: benzyl acetate or methyl phenylacetate?Place a CH₂ between an ester oxygen and a phenyl ring from ¹H chemical shifts (benzyl acetate).
Work backward 2
- Build a structure from symmetric setsIntegrate DEPT, proton splitting and exchange into an alcohol assignment.
- C₆H₁₄O with a septet and a doublet: diisopropyl etherUse symmetry and splitting to assemble a C₆H₁₄O ether from two ¹H and two ¹³C signals.
Plan a synthesis 3
- Plan a positional-isomer testUse carbon-environment symmetry to distinguish two aromatic positional isomers.
- C₆H₁₂O alcohol: plan a ring vs C=C testPlan the single observation that decides whether a C₆H₁₂O alcohol's unsaturation is a ring or a C=C.
- Which test separates butanal and butanone?Choose the measurement that distinguishes two isomers sharing formula and carbonyl.
Explain why 3
- Explain why a formula is not a structureRecognize underdetermination when two carbonyl isomers share supplied evidence.
- State the boundary of a structure assignmentDistinguish constitution from absolute configuration using achiral spectral data.
- trans-Hex-3-ene: why no C=C band in the IR?Explain why a missing C=C stretch does not prove a ring when NMR shows a symmetric alkene (trans-hex-3-ene).
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