Discussion
The spectroscopic data for an organic compound with molecular formula C10H12O2 are given below.
IR band around 1750 cm-1, 1H NMR δ 7.3 (m, 5H), 5.85 (q, 1H, J = 7.2 Hz), 2.05 (s, 3H), 1.5 (d, 3H, J = 7.2 Hz) ppm. The compound is
Answer: B
The compound is 1-(phenylethyl) acetate, CH3COOCH(CH3)C6H5.
Read the data piece by piece. The IR band near 1750 cm-1 is an ester carbonyl. 7.3 (5H, m) is a monosubstituted benzene ring. 2.05 (3H, s) is an acetyl CH3 with no neighbours. 1.5 (3H, d) and 5.85 (1H, q), with the same J of 7.2 Hz, are a CH-CH3 pair coupled to each other. A CH as far downfield as 5.85 ppm must sit on an oxygen and a phenyl ring at once, which is exactly the benzylic CH-O-C(O)CH3 of 1-phenylethyl acetate.
Methyl 2-phenylpropionate would show an OCH3 singlet near 3.7 ppm and its CH quartet near 3.7, not 5.85. 2-Phenylethyl acetate and methyl 3-phenylpropionate have CH2CH2 chains, which give two triplets and no quartet-doublet pair.
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