Table 2. Enthalpy changes for the H-bond competing processes (A + B ↔ C + D) of strong ionic H-bonds (ΔH, in kilocalories per mole).
On the basis of the H-bond energies given (25), we list H-bond competing processes, the energy of each H-bond, and the enthalpy change (ΔH) of each process. The strongest H-bond of each process is D, which is on the right side of the process. Because all processes have negative ΔH values, we conclude that the reversible H-bond competing process favors the s-s/w-w H-bond pairing in enthalpy. A, B, C, and D denote the hydrogen bonds of the H-bond competing processes. EA, EB, EC, and ED denote the hydrogen bond energy of A, B, C, and D in kilocalories per mole.
| A | B | C | D | EA | EB | EC | ED | ΔH | |
| 1 | Cl…H-Cl | F…H-F | Cl…H-F | F…H-Cl | 23.1 | 38.6 | 21.8 | 59.8 | −19.9 |
| 2 | Cl…H-Br | F…H-F | Cl…H-F | F…H-Br | 29.0 | 38.6 | 21.8 | 65.0 | −19.2 |
| 3 | Cl…H-I | F…H-F | Cl…H-F | F…H-I | 32.0 | 38.6 | 21.8 | 72.0 | −23.2 |
| 4 | Cl…H-CN | F…H-F | Cl…H-F | F…H-CN | 21.0 | 38.6 | 21.8 | 39.5 | −1.7 |
| 5 | Br…H-Cl | F…H-F | Br…H-F | F…H-Cl | 19.0 | 38.6 | 17.0 | 59.8 | −19.2 |
| 6 | Br…H-Br | F…H-F | Br…H-F | F…H-Br | 20.0 | 38.6 | 17.0 | 65.0 | −23.4 |
| 7 | Br…H-CN | F…H-F | Br…H-F | F…H-CN | 16.0 | 38.6 | 17.0 | 39.5 | −1.9 |
| 8 | I…H-Cl | F…H-F | I…H-F | F…H-Cl | 13.0 | 38.6 | 15.0 | 59.8 | −23.2 |
| 9 | CN…H-Cl | F…H-F | CN…H-F | F…H-Cl | 37.0 | 38.6 | 21.1 | 59.8 | −5.3 |
| 10 | F…H-F | CN…H-Br | CN…H-F | F…H-Br | 38.6 | 42.0 | 21.1 | 65.0 | −5.5 |
| 11 | CN…H-CN | F…H-F | CN…H-F | F…H-CN | 20.0 | 38.6 | 21.1 | 39.5 | −2.0 |
| 12 | Cl…H-I | F…H-Cl | Cl…H-Cl | F…H-I | 32.0 | 59.8 | 23.1 | 72.0 | −3.3 |
| 13 | Cl…H-Cl | F…H-CN | Cl…H-CN | F…H-Cl | 23.1 | 39.5 | 21.0 | 59.8 | −18.2 |
| 14 | Br…H-Br | F…H-Cl | Br…H-Cl | F…H-Br | 20.0 | 59.8 | 19.0 | 65.0 | −4.2 |
| 15 | Br…H-Cl | F…H-CN | Br…H-CN | F…H-Cl | 19.0 | 39.5 | 16.0 | 59.8 | −17.3 |
| 16 | CN…H-Cl | F…H-CN | CN…H-CN | F…H-Cl | 37.0 | 39.5 | 20.0 | 59.8 | −3.3 |
| 17 | Cl…H-I | F…H-Br | Cl…H-Br | F…H-I | 32.0 | 65.0 | 29.0 | 72.0 | −4.0 |
| 18 | Cl…H-Br | F…H-CN | Cl…H-CN | F…H-Br | 29.0 | 39.5 | 21.0 | 65.0 | −17.5 |
| 19 | Br…H-Br | F…H-CN | Br…H-CN | F…H-Br | 20.0 | 39.5 | 16.0 | 65.0 | −21.5 |
| 20 | F…H-CN | CN…H-Br | CN…H-CN | F…H-Br | 39.5 | 42.0 | 20.0 | 65.0 | −3.5 |
| 21 | Cl…H-I | F…H-CN | Cl…H-CN | F…H-I | 32.0 | 39.5 | 21.0 | 72.0 | −21.5 |
| 22 | Br…H-Br | Cl…H-F | Br…H-F | Cl…H-Br | 20.0 | 21.8 | 17.0 | 29.0 | −4.2 |
| 23 | I…H-Cl | Cl…H-F | I…H-F | Cl…H-Cl | 13.0 | 21.8 | 15.0 | 23.1 | −3.3 |
| 24 | CN…H-F | Cl…H-Cl | Cl…H-F | CN…H-Cl | 21.1 | 23.1 | 21.8 | 37.0 | −14.6 |
| 25 | CN…H-F | Cl…H-Br | Cl…H-F | CN…H-Br | 21.1 | 29 | 21.8 | 42.0 | −13.7 |
| 26 | Br…H-Br | Cl…H-Cl | Br…H-Cl | Cl…H-Br | 20.0 | 23.1 | 19.0 | 29.0 | −4.9 |
| 27 | CN…H-CN | Cl…H-Cl | Cl…H-CN | CN…H-Cl | 20.0 | 23.1 | 21.0 | 37.0 | −14.9 |
| 28 | Br…H-Br | Cl…H-CN | Br…H-CN | Cl…H-Br | 20.0 | 21.0 | 16.0 | 29.0 | −4.0 |
| 29 | CN…H-CN | Cl…H-Br | Cl…H-CN | CN…H-Br | 20.0 | 29.0 | 21.0 | 42.0 | −14.0 |
| 30 | I…H-Cl | Br…H-F | I…H-F | Br…H-Cl | 13.0 | 17.0 | 15.0 | 19.0 | −4.0 |
| 31 | Br…H-Cl | CN…H-F | Br…H-F | CN…H-Cl | 19.0 | 21.1 | 17.0 | 37.0 | −13.9 |
| 32 | Br…H-Br | CN…H-F | Br…H-F | CN…H-Br | 20.0 | 21.1 | 17.0 | 42.0 | −17.9 |
| 33 | Br…H-Br | CN…H-Cl | Br…H-Cl | CN…H-Br | 20.0 | 37.0 | 19.0 | 42.0 | −4.0 |
| 34 | Br…H-Cl | CN…H-CN | Br…H-CN | CN…H-Cl | 19.0 | 20.0 | 16.0 | 37.0 | −14.0 |
| 35 | CN…H-CN | Br…H-Br | Br…H-CN | CN…H-Br | 20.0 | 20.0 | 16.0 | 42.0 | −18.0 |
| 36 | I…H-Cl | CN…H-F | I…H-F | CN…H-Cl | 13.0 | 21.1 | 15.0 | 37.0 | −17.9 |