Table 1. Experimental Deprotonation Enthalpies (ΔacidH°), Entropies (ΔacidS°), and Gas Phase Acidities (GA) of 5,5-Alkylbarbituric Acids.
| GAtheora,d |
|||||
|---|---|---|---|---|---|
| ΔacidH0a | ΔacidS0b | GAa,c | G3 | G4 | |
| barbituric acid (C–H) | 1368.6 ± 10.0 | 125.5 ± 8.4 | 1330.9 ± 10.0 | 1332.6 | 1334.7 |
| barbituric acid (N–H) | 1389.1 ± 10.5 | 93.7 ± 8.4 | 1361.5 ± 10.5 | 1364.4 | 1369.8 |
| 5,5-dimethylbarbituric acid, 2 | 1404.2 ± 8.8 | 106.7 ± 8.4 | 1369.4 ± 8.8 | 1371.5 | 1369.0 |
| 5,5-diethylbarbituric acid, 3 | 1397.9 ± 8.8 | 98.7 ± 8.4 | 1368.2 ± 8.8 | 1367.7 | 1366.5 |
a
All values are given in kJ mol–1.
b
In J mol–1 K–1.
c
Derived from equation ΔG = ΔH – TΔS, with T = 298.15 K.
d
GA theoretical values calculated at G3 and G4 levels of theory.