Table 1. DFT-Computed Activation Energies (ΔE298⧧), Reaction Enthalpies (ΔH298), and Reaction Free Energies (ΔG298) for CO2 Loss from Z–CO2• Radicals at 298 Ka.
| radical | methodb | ΔE298⧧ | ΔH298 | ΔG298 | Eexpt⧧ |
|---|---|---|---|---|---|
| Et2N–CO2• | A | 1.3 | –8.8 | –20.2 | – |
| B | 0.7 | –5.5 | –16.8 | ||
| EtNH–CO2• | A | 6.5 | –5.5 | –15.6 | – |
| B | 7.4 | –4.7 | –14.7 | ||
| NH2–CO2• | A | 11.6 | –1.2 | –9.5 | – |
| B | 11.8 | –3.5 | –12.1 | ||
| EtO–CO2• | A | 11.5 | –7.8 | –18.9 | ∼13c |
| B | 16.1 | –3.9 | –13.8 | ||
| Et–CO2• | A | [0.4]d | –16.5 | –28.6 | ∼1.7e |
| B | –d | –14.6 | –24.8 |
a
Energies in kcal mol–1 are reported.
b
Method A: UB3LYP/cc-pvtz level including corrections to 298 K. Method B: CBS-QB3 level.
c
Value for primary RCH2OC(O)O• radicals (see ref (4b)).
d
A well-defined transition state was not found with the cc-pvtz basis set or at the CBS-QB3 level. A ΔE298⧧ value of 0.44 kcal mol–1 was obtained for a transition state located with the 6-31G(d) basis set.
e
See ref (12).