04-BS-12 · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exam 04-BS-12, Organic Chemistry — May 2019 sitting (the page-1 header and the running footer, "04-BS-12/May 2019", both give the date). 3 hours, closed-book examination; one Casio/Sharp-approved calculator permitted. NOTES on page 1 state that TEN (10) questions constitute a complete exam paper and only the first 10 as they appear in the answer book are marked, but this sitting prints 13 numbered questions — every question and sub-part below is answered in full.
Reference texts: McMurry, Organic Chemistry, 9th ed. (acid/base theory, functional-group identification, SN1/SN2 mechanisms and stereochemistry, alkyne/acetylide synthesis, electrophilic aromatic substitution, IR/NMR/mass-spectral structure elucidation, named-drug synthesis design, and step-growth polymer chemistry). Every molecular formula, exact mass, and stereochemical (R/S, cis/trans) assignment below.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Approach. Each compound carries a different, largely non-overlapping set of diagnostic IR group frequencies (O–H breadth, presence/absence and exact position of C=O, aromatic ring bands, C–O fingerprint pattern) — match every spectrum on its single most distinctive feature first, then use the remaining fingerprint-region complexity to break any tie.
| Compound | Diagnostic IR features | Spectrum |
|---|---|---|
| A (carboxylic acid) | very broad, deep O–H envelope ≈2500–3300 cm−1 (strong intermolecular H-bonded dimer) superposed on the C–H stretch, plus a strong, sharp C=O ≈1710 cm−1 | [5] |
| F (3° alcohol) | a broad but much narrower, rounded O–H band ≈3300–3550 cm−1 (H-bonded, monomeric/dimeric, not acid-broad); no C=O anywhere | [2] |
| E (ester) | no O–H at all; one strong, sharp C=O ≈1730–1750 cm−1 (esters sit higher than ketones/acids) plus a busy, strong C–O–C fingerprint (2 bands, 1000–1300 cm−1) | [4] |
| D (ether) | no O–H, no C=O; only C–H stretches plus a single strong, simple C–O–C stretch (≈1100–1150 cm−1, often split for a branched diisopropyl ether) — the simplest fingerprint of the six | [6] |
| C (aromatic, cumene) | no O–H, no C=O; weak aromatic overtone/combination bands ≈1660–2000 cm−1, ring C=C stretches ≈1500 and 1600 cm−1, and strong monosubstituted-ring out-of-plane bending ≈690–770 cm−1 | [3] |
| B (terminal alkene) | no O–H, no C=O, no aromatic bands; weak =C–H stretch just above 3000 cm−1, weak C=C ≈1650 cm−1, and a diagnostic =CH2 out-of-plane wag ≈890 cm−1 | [1] |
