123
Answer:
 |
Reasoning:
| Isomer | Number of signals | Irel. | Multiplicity | |
|---|---|---|---|---|
| 1. | H2C=CH-CH2-CH2-CH3 | 6 | ||
| 2. | H3C-CH=CH-CH2-CH3 | 5 | 3 : 1 : 1 : 2 : 3 | 2 / 8 / 6 / 8 / 3 |
| 3. |  |
5 | 1 : 1 : 1 : 1 : 6 | |
| 4. |  |
5 | 1 : 1 : 3 : 2 : 3 | 2 / 2 / 1 / 4 / 3 |
| 5. |  |
4 |
The isomer 4 is the best fit for the spectrum. The problem was complicated by the fact that the two protons H2C= are exposed to very similar chemical environments, and therefore show very similar chemical shifts.
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