Table 2.
Carbonyl stretching frequencies, donor–acceptor geometries and interaction energies, and hydrolytic stabilities of compounds 1a–e and 2a–e.
| Probe | νC=O (cm−1)a | dX···C (Å)b | θX···C=O (°)b | En→π* (kcal/mol)b | ΔEX,C=O (kcal/mol)b | t1/2 (h)c |
|---|---|---|---|---|---|---|
| 1a | 1766 | 3.06 | 80.9 | — | 0.20 | 4.7 |
| 1b | 1774 | 2.97 | 77.0 | 0.22 | 0.85 | 1.8 |
| 1c | 1774 | 3.25 | 84.7 | 0.54 | 0.98 | 11 |
| 1d | 1776 | 3.50d, 3.55e | 91.0d, 92.1e | 0.25d, 0.33e | 0.46d, 0.54e | 33 |
| 1e | 1774 | 3.62d, 3.65e | 91.0d, 92.1e | 0.40d, 0.44e | 0.81d, 1.01e | >2,000 |
| 2a | 1766 | 3.41 | 85.1 | — | 0.11 | ND |
| 2b | 1770 | 3.27 | 85.9 | 0.22 | 0.19 | ND |
| 2c | 1774 | 3.00 | 85.8 | 0.51 | 1.10 | ND |
| 2d | 1772 | 3.13 | 87.6 | 0.52 | 1.17 | ND |
| 2e | 1767 | 3.59 | 91.1 | 0.51 | 1.03 | ND |
a
Measured with FT-IR spectroscopy.
b
Calculated for each X···C=O interaction in the optimized geometry.
c
Experimental half-life for spontaneous hydrolysis in OptiMEM containing FBS (10% v/v).
d
Data for 4′,5′-halo substituents.
e
Data for 2′,7′-halo substituents.
ND, not determined.