Table 2.

Brønsted coefficients, β_lg, from experiments and calculation. The experimental coefficients, ${\beta }_{lg}^1$ and ${\beta }_{lg}^2$ were measured for transesterification reactions with aryl and alkyl leaving groups, respectively. The calculated coefficients, ${\beta }_{lg}^1$ and ${\beta }_{lg}^2$ were determined from theoretical rates derived from early and late transition states (TS1 and TS2), respectively, of the series of model reactions described in Scheme 1-2.

	Model System	${\beta }_{lg}^1$	${\beta }_{lg}^2$	β eq	Temp (°C)	Ref./Model
Expt.	Uridine 3′-phosphate	−0.54	−1.28	· · ·	25	33,56
	Uridine 3′-phosphate	−0.52	−1.34	· · ·	25	55
	Uridine 3′-phosphate	· · ·	−1.10	· · ·	65	75
	2-hydroxypropyl phosphatea	−0.52	−1.09	· · ·	80	58,55
	Guanosine 3′-phosphate	−0.38	· · ·	· · ·	35	76
	Phosphono monoanion	· · ·	· · ·	−1.74	25	57
Calc.	2-hydroxyethyl phosphate	−0.54	−2.04	−2.44	25	UFF
	2-hydroxyethyl phosphate	−0.54	−2.03	−2.44	80	UFF
	2-hydroxyethyl phosphate	−0.52	−1.37	−1.74	25	UAKS
	2-hydroxyethyl phosphate	−0.52	−1.32	−1.74	80	UAKS

^aLinear Brønsted correlation coefficients (${\beta }_{lg}^1$ and ${\beta }_{lg}^2$) were calculated from limited data⁵⁸ using adjusted pK_a values,⁵⁵ and may not be statistically reliable.