Table 1. Stability Constants for 1 with neutral substrate added K (M-1)a
| Neutral guest |
Stability constant (M-1) |
| methanol |
12.7 ± 1.0 |
| ethanol |
10.7 ± 0.7 |
| benzyl alcohol |
9.7 ± 0.7 |
| isopropyl alcohol |
7.0 ± 0.4 |
| sec-butanol |
6.2 ± 0.4 |
| N-formylglycine ethyl ester |
13.3 ± 1.0 |
| N,N-dimethylformamide |
11.3 ± 0.8 |
| N,N-dimethylacetamide |
9.0 ± 0.9 |
| 1,1,3,3-tetramethylurea |
2.2 ± 0.1 |
| dimethyl sulfoxide |
16.2 ± 1.1 |
| 1,2-dimethylimidazole |
5.4 ± 0.3 |
| acetone |
2.2 ± 0.2 |
| nitromethaneb |
- |
a In benzene-d6 at 298 K. For each titration, the concentration of 1 was held constant (at ca. 4 x 10-3 M) as aliquots of the substrate in benzene-d6 (ca. 1 M) were added. b In this instance, the induced shifts in the NH proton(s) of 1 were too small (< 0.15 ppm) to afford a reliable Ka value.