Table 4. Carbon-13 and Nitrogen-15 Chemical Shifts for Forms I, III, and V.
| form | C4/6a | C2b | C5 | C7/9 | C8/10 | N |
|---|---|---|---|---|---|---|
| III | 178.4/177.7 | 148.0 | 58.6 | 33.3 | 9.9 | –226.7 |
| I0 | 176.5/175.7 | 152.7 | 58.8 | 34.8 | 9.6 | –226.5 |
| 173.4/172.7 | 31.8 | 9.0 | –228.5 | |||
| V | 180.3/179.7 | 149.0 | 58.4 | 34.4–32.0c | 10.3–9.0d | –223.5e |
| 172.1/171.4 | 57.9 | –227.1e |
The doublet splittings for I0 and III are caused by second-order effects of coupling to one 14N nucleus. This also affects the splittings of V. The true chemical shifts (in ppm) lie closer to the more intense (low-frequency) components.
The apparent triplet splitting arises from the second-order effects of coupling to two 14N nuclei.
In principle, there are 8 signals. Four maxima of differing intensities can be observed.
In principle, there are 8 signals. Three maxima of differing intensities, together with a shoulder can be observed. Deconvolution results are consistent with the existence of 8 signals (see Figure S5 in the Supporting Information).
The signals are in an approximately 3:5 intensity ratio. In principle, there should be 8 resonances.