Discussion
The compound that shows the following spectral data is :
1H-NMR (ppm) : 3.79 (s, 3H), 7.29 (d, J = 8Hz, 1H), 8.47 (dd, J = 8 and 2Hz, 1H), 9.11 (d, J = 2Hz, 1H).
Answer: A
The compound is 1-methoxy-2,4-dinitrobenzene (2,4-dinitroanisole).
The singlet at 3.79 (3H) is the OCH3. The three aromatic protons show the pattern of a 1,2,4-trisubstituted ring:
- 9.11 (d, J = 2 Hz): H-3, between the two nitro groups, coupled only meta to H-5 and most deshielded.
- 8.47 (dd, J = 8 and 2 Hz): H-5, ortho to H-6 and meta to H-3.
- 7.29 (d, J = 8 Hz): H-6, ortho to the methoxy group and so the most shielded.
2,6-Dinitroanisole is symmetric and would show only two aromatic signals (a 2H doublet and a 1H triplet). In 3,4- and 2,5-dinitroanisole no proton lies between two nitro groups, so neither can give a signal as far downfield as 9.11; and in the 2,5-isomer the 8 Hz doublet belongs to H-3, ortho to a nitro group, which would appear far downfield rather than at 7.29.
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