Table 1.

Proton transfer activation energy^a (ΔE), enthalpy (ΔH) and free energy (ΔG) (in kcal/mol) calculated using different methods with zero point energy (ZPE) correction.

System	Activation barrier (ΔE)		ΔHb	ΔGb
	forward	backward
G•+-C+11H2Oc	1.42	2.59	−1.32	−0.65
G•+-C+6H2Oc	2.60	1.67	1.04	0.90
G•+-Cc	2.21	0.76	1.45	1.38
G•+-Cd	2.96	1.58	1.38	1.38
G•+-Ce	4.26e	3.04e	1.30	1.30
G•+-Cf	-	-		1.6f
G•+-Cg	-	-	-	1.18g

^aEnergies were calculated considering G^•+-C as reference, see Figure 1.

^bEnthalpy (ΔH) and free energy (ΔG) changes calculated at 298 K with ZPE correction in kcal/mol.

^cPresent calculation using B3LYP/6-31+G**.

^dB3LYP/6-31+G* (ref. ¹⁴).

^eB3LYP/6-31G** and without ZPE correction (ref. ¹¹).

^fZPE corrected ΔE calculated using UB3LYP/D95*//UHF/6-31G* (ref. ¹⁰).

^gHF/3-21G* (ref. ¹³).