Discussion
The correct match for the protons labeled in compound X in Column M with the corresponding chemical shifts (δ, ppm) in Column N is
| Column M | Column N | ||
|---|---|---|---|
| P | Ha | I | 7.00 (ddd, J = 8.4, 7.3, 1.4 Hz, 1H) |
| Q | Hb | II | 7.17 (dd, J = 8.4, 1.4 Hz, 1H) |
| R | Hc | III | 7.59 (ddd, J = 8.4, 7.3, 1.4 Hz, 1H) |
| S | Hd | IV | 8.12 (dd, J = 8.4, 1.4 Hz, 1H) |
Answer: A
The correct match is P → II; Q → III; R → I; S → IV.
Compound X is 2-nitrophenol. Use the splitting first: a proton with two ortho neighbours appears as a ddd (two ortho couplings, 8.4 and 7.3 Hz, and one meta), while a proton with one ortho neighbour is a dd. Ha and Hd each have only one ortho neighbour, so they are the two dd signals; Hb and Hc are the ddd signals.
- Hd is ortho to the strongly withdrawing NO2, so it is the most deshielded dd: 8.12 (IV).
- Ha is ortho to the donating OH, the shielded dd: 7.17 (II).
- Hb is para to NO2, the deshielded ddd: 7.59 (III).
- Hc is para to OH, the shielded ddd: 7.00 (I).
Every other option breaks the splitting rule by giving a dd proton a ddd signal (P → I, or Q → IV), or swaps Hb and Hc, ignoring that the para nitro group deshields Hb.
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