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Spectroscopy · Part 1 of 4
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Name the three spectroscopic techniques assessed in this standard and state which aspect of structure each is best at determining.
Explain why no single spectroscopic technique is sufficient to determine an organic structure, using an example.
Justify the distinction between determining a structure and justifying a structure in this standard, and explain what an Excellence answer must contain that a Merit answer does not.
A mass spectrum shows its highest significant peak at m/z 58 and its tallest peak at m/z 43. Identify the molar mass and explain the difference between the molecular ion peak and the base peak.
A compound has a molecular ion at m/z 60 and an IR spectrum showing a very broad absorption from 2500–3000 cm−1 and a strong peak at 1715 cm−1. Determine the molecular formula and structure, showing your reasoning.
A student reports that a compound with a molecular ion at m/z 45 must contain oxygen because 45 is an odd number. Justify whether this reasoning is sound, and explain what an odd molar mass actually indicates.
Explain how the mass spectrum distinguishes a compound containing chlorine from one containing bromine.
A compound with molecular ion at m/z 72 shows strong fragments at m/z 57 and m/z 43. Its IR shows a strong absorption at 1715 cm−1 and nothing above 3000 cm−1. Determine the structure, explaining how the fragments support your answer.
Two compounds both have a molecular ion at m/z 60. One shows a strong fragment at m/z 45 and one at m/z 31. Justify what each fragment indicates, and integrate this with what IR data would be needed to confirm each structure.