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Functional Groups: Classification of Organic Compounds · Paper 2 — Free Chemistry HL Practice Questions

1ChallengeSAQ-LIUPAC naming conventions for organic compounds7 marksPaper 2~11 min

Data

Proton environment — Typical δ\delta / ppm — Multiplicity rule R–OH — 0.5–5.00.5\text{–}5.0 (broad) — exchangeable R–CH‾(OH)–R\text{R–}\underline{\text{CH}}\text{(OH)–R} — 3.5–4.53.5\text{–}4.5 — n+1n+1 R–CH‾3\text{R–C}\underline{\text{H}}_3 — 0.8–1.20.8\text{–}1.2 — n+1n+1 R–CH‾2–R\text{R–C}\underline{\text{H}}_2\text{–R} — 1.2–1.51.2\text{–}1.5 — n+1n+1 R–CH‾–R\text{R–C}\underline{\text{H}}\text{–R} — 1.5–2.01.5\text{–}2.0 — n+1n+1 Relative atomic masses: Ar(H)=1.01A_r(\text{H}) = 1.01, Ar(C)=12.01A_r(\text{C}) = 12.01, Ar(O)=16.00A_r(\text{O}) = 16.00
A student attempts to synthesize 3-methylpentan-2-ol via a Grignard reaction. The isolated product is analysed by 1H^1\text{H} NMR spectroscopy and mass spectrometry. Spectral data for the isolated product: - Mass spectrum: molecular ion at m/z=102m/z = 102 - 1H^1\text{H} NMR: δ 0.85 ppm\delta\ 0.85\ \text{ppm} (3H3\text{H}, triplet); δ 1.15 ppm\delta\ 1.15\ \text{ppm} (3H3\text{H}, doublet); δ 1.30–1.55 ppm\delta\ 1.30\text{–}1.55\ \text{ppm} (4H4\text{H}, multiplet); δ 1.60 ppm\delta\ 1.60\ \text{ppm} (1H1\text{H}, broad singlet, exchangeable with D2O\text{D}_2\text{O}); δ 3.80 ppm\delta\ 3.80\ \text{ppm} (1H1\text{H}, quartet, J=6.5 HzJ = 6.5\ \text{Hz}) Reference
(a)
Show that the molecular formula of the isolated product is C6H14O\text{C}_6\text{H}_{14}\text{O}, and determine the degree of unsaturation. Hence state what the degree of unsaturation indicates about the compound. [3 marks]
(b)
Explain why the 1H^1\text{H} NMR data are inconsistent with the proposed structure of 3-methylpentan-2-ol, and deduce the structural fragment directly implied by the signal at δ 3.80 ppm\delta\ 3.80\ \text{ppm}. [3 marks]
(c)
Evaluate whether the combination of 1H^1\text{H} NMR spectroscopy and mass spectrometry is sufficient to distinguish definitively between all structural isomers of C6H14O\text{C}_6\text{H}_{14}\text{O}. [1 mark]
diagram

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