04-BS-12 · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exam 04-BS-12, Organic Chemistry — May 2018. 3 hours, closed-book examination (one Casio/Sharp-approved calculator and one hand-written aid sheet 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. (drug acid–base/salt pharmacokinetics, steroid/bile-acid amphiphilicity, arene-oxide metabolism, cyclopropane stereochemistry and CIP assignment, reaction-energy diagrams, ester equilibria and intramolecular effective molarity, SN2 stereochemistry at a common stereocentre, named-drug synthesis design, epoxide ring-opening stereochemistry, mass-spectral formula discrimination, opioid IR/NMR structure elucidation, keto–enol tautomerism and conjugation/acidity, and condensation-polymer monomer identification). Every molecular formula, mass-balance, exact-mass, and stereochemical (R/S) 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.
a) 1,4-Cyclohexanediol + glutaric acid → polyester. Each –OH reacts with a –COOH (Fischer-type esterification, −H2O per bond), alternating diol and diacid units indefinitely:
b) Terephthaloyl chloride + 1,6-diaminohexane → polyamide. Each –NH2 reacts with an acid chloride (−HCl per bond, faster and more irreversible than using the free diacid), giving an aromatic nylon (poly(hexamethylene terephthalamide)):
Monomers from the drawn polymers. Reading each ester linkage backward (break every C(=O)–O bond and add back –OH to each fragment): the first polymer's repeat unit shows an ester alternating between an –O–CH2CH2–O– diol fragment and a –C(=O)–CH=CH–C(=O)– diacid fragment with a trans double bond — the monomers are ethylene glycol and fumaric acid (the trans unsaturated diacid; its cis isomer, maleic acid, would draw with the two ester groups on the same side of the double bond, not the diagonal trans arrangement shown).
The second polymer's repeat unit shows an ester alternating between a 1,2-disubstituted (ortho) benzene diacid fragment and a –O–CH2CH2–O–CH2CH2–O– diether-diol fragment — the monomers are phthalic acid (the ortho isomer, not terephthalic acid's para) and diethylene glycol.
