Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exam 04-BS-12, Organic Chemistry — December 2017. 3 hours, closed-book
examination (no calculator required); 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
strength of drugs, pharmacokinetics/lipophilicity, β-lactam reactivity, SN2
stereochemistry, Williamson-ether-type syntheses, alkyne alkylation, IR/NMR structure
elucidation, radical vs. ionic HBr addition, electrophilic aromatic substitution & synthesis
design, acid strength/resonance & induction, polymer/monomer identification). Every molecular
formula, mass balance, and stereochemical (R/S) assignment below.
Check: the six condensed formulas are read bond-by-bond from the drawn structures. Compound A is drawn with a carbonyl double bond and terminal –OH — i.e. butanoic acid, CH3CH2CH2C(=O)OH, not an alcohol (1-butanol) — and compound B's chain carries four CH2 units after the branch point (2-methylhex-1-ene, C7H14), not three. Reading A as an alcohol would invert the O–H-region reasoning for compound A (alcohol vs. acid bands are qualitatively different) below.
Label
Compound (corrected)
Formula
Key functional group
A
butanoic acid, CH3CH2CH2C(=O)OH
C4H8O2
carboxylic acid
B
2-methylhex-1-ene, CH2=C(CH3)CH2CH2CH2CH3
C7H14
terminal alkene
C
cumene (isopropylbenzene), C6H5CH(CH3)2
C9H12
aromatic ring, no C=O/OH
D
diisopropyl ether, (CH3)2CHOCH(CH3)2
C6H14O
ether
E
tert-butyl acetate, CH3C(=O)OC(CH3)3
C6H12O2
ester
F
triethylmethanol (given), (CH3CH2)3COH
C7H16O
3° alcohol
Approach. Work spectrum-by-spectrum from the most diagnostic (rarest/most
distinctive) absorptions first — the broad carboxylic-acid O–H, the sharp ester C=O,
the aromatic ring-stretch pair, and the alkene's C=C/vinylic C–H — leaving the two
featureless aliphatic spectra (ether, tertiary alcohol) to be distinguished last by their O–H
presence/absence.
Spectrum [5] → A (butanoic acid). This is the only spectrum with the
unmistakable carboxylic-acid signature: a very broad, deep O–H absorption spanning
roughly 2500–3300 cm−1 (H-bonded carboxylic-acid dimer, far broader than any
simple alcohol O–H) merging directly into the C–H stretches, plus a strong, sharp C=O
band near 1710 cm−1 (conjugated with the O–H, hydrogen-bonded acid C=O sits
lower than an ester's).
Spectrum [4] → E (tert-butyl acetate, ester). No O–H at all, but a
strong, sharp carbonyl band appreciably higher than the acid's (esters absorb
≈1735–1750 cm−1, since there is no H-bonding to lower the C=O force
constant), plus the two strong C–O–C stretch bands (asymmetric/symmetric,
≈1150–1250 cm−1) characteristic of an ester's acyl-oxygen linkage.
Spectrum [3] → C (cumene, aromatic). No O–H, no C=O; instead a weak
C–H stretch just above 3000 cm−1 (aromatic/vinylic C–H) and the
diagnostic pair of aromatic ring-stretch bands near 1600 and 1500 cm−1, unique to
the benzene ring.
Spectrum [6] → B (2-methylhex-1-ene, alkene). A weak absorption just
above 3000 cm−1 (vinylic =C–H, weaker/sharper than an aromatic C–H),
a medium C=C stretch near 1640–1650 cm−1, and a dense cluster of aliphatic
C–H bending/fingerprint peaks reflecting the longer saturated chain — no O–H, no
C=O, no aromatic pair.
Spectrum [2] → F (triethylmethanol, 3° alcohol). A broad, moderately
deep O–H band centred near 3300–3400 cm−1 (hydrogen-bonded alcohol,
narrower and shallower than the acid's in spectrum [5]) with no accompanying carbonyl anywhere in
the fingerprint region.
Spectrum [1] → D (diisopropyl ether), by elimination. No O–H, no
C=O, no aromatic pair, no alkene C=C — the only remaining candidate, confirmed by the very
strong, broad C–O–C asymmetric-stretch band near 1100–1150 cm−1
(the single most intense feature in the whole spectrum, as expected for a simple dialkyl
ether).
