Table 1. Selected spectroscopic properties for twisted amides 4·HBF4 and 4·BF3 and for the hydrolysis product isonipecotic acid tetrafluoroborate (11).
| Compounda | 4·HBF4 | 4·BF3 | 11 |
|---|---|---|---|
| δ1H of NHx | 7.76 (t, 1J1H14N = 63 Hz) | − | 6.90-6.12 (m, 1J1H14N = ∼55 Hz) |
| δ13C of C=O | 174.7 | 179.8 | 169.7 |
| δ11B | −1.2 (s) | −0.3 (q, 1J11B19F = 13.8 Hz) | −1.2 (s) |
| δ19F | −151.3 (s) | −154.9 (q, 1J19F11B = 13.9 Hz) | −151.2 (s) |
| δ14N | 34.8 (d, 1 J14N1H = 62.8 Hz) | 39.3 (s) | −4.9 (m, 1J14N1H = not resolved) |
| δ15Nb | 78.6 (1J15N1H = ∼88 Hz) | − | 38.8 (1J15N1H = ∼77 Hz)c |
| IR, νmax C=O, cm-1 | 1877d | 1860d | 1814e |
a
All NMR spectra were recorded in CD3CN.
b
Due to the low abundance of this isotope, the chemical shifts and coupling constants were determined by 1H-15N and 1H{15N}-15N correlation experiments.
c
A vicinal proton coupling constant of 2J1H1H = 10.8 Hz was observed.
d
Measured using an ATR-IR in an argon filled glovebox.
e
Neat film on a NaCl plate.