Chemisode Spectra LabVCE Chemistry learning simulation
Final investigation

Spectra investigation: identify an unknown

Use composition data and unlabelled MS, IR, ¹³C NMR and ¹H NMR spectra to identify one of 20 unknown organic compounds.

How to investigate

1 CompositionUse combustion data or percentage composition to determine an empirical formula.
2 Mass spectrumEstimate molecular mass and recognise useful isotope patterns.
3 IR spectrumUse the spectrum to infer bonds and possible functional groups.
4 ¹³C NMRCount carbon environments and use chemical shift.
5 ¹H NMRUse environments, integration, splitting and chemical shift to connect the structure.
Evidence-first design: the spectra are not annotated with the molecular ion, base peak, functional group, peak assignments or key chemical shifts. Those conclusions are for you to make.

Choose an unknown

Unknowns 1–20 range from foundation examples to isomers, halogenated compounds, amines, an amino acid and a branched alkane.

Unknown 1

Select each evidence source and interpret the raw data.

Evidence only: interpret the spectra yourself.

Evidence display

Record your analysis

Composition calculations

For C/H/O-only combustion data, use n(C) = n(CO₂) and n(H) = 2 · n(H₂O). Oxygen can then be found by mass difference because the case explicitly states that only C, H and O are present.

For percentage-composition cases, imagine a 100 g sample so each percentage becomes a mass in grams, convert each element to mole, then divide by the smallest amount.

Use all the evidence

Do not identify a molecule from one spectrum alone. The final structure must agree with composition, molecular mass, IR evidence, the number and positions of ¹³C environments, and the ¹H pattern.

Halogenated cases include the characteristic isotope evidence from Cl-35/Cl-37 or Br-79/Br-81.