Table 2. Comparison of pK_a,0 of Analyte Molecules Determined by ¹H CSI with Literature Values.

50%1-propanol/H2O				50% DMSO/H2O				30% CD3CN/H2O
analyte	indicator	pKa,0 NMR	pKa,0Lit	analyte	indicator	pKa,0 NMR	pKa,0 Lit	analyte	indicator	pKa,0 NMR	pKa,0Lit
salicylic acida	2,6-DHB, triazole, glycolate, acetate	4.12 ± 0.37	4.1717	salicylic acida	2,6-DHB, triazole, DMG, glycolate, acetate	3.46 ± 0.21	3.488	salicylic acida	2,6-DHB, triazole, DMG, glycolate, acetate	3.69 ± 0.42	3.43,27 3.74,28 3.9329
benzoic acidb	2,6-DHB, triazole, glycolate, acetate, 2MI	5.52 ± 0.38	5.507	benzoic acid	triazole, glycolate, acetate, 2MI	5.25 ± 0.31	5.23,8 5.7330	benzoic acid	triazole, glycolate, acetate, 2MI	5.10 ± 0.49	4.78,31 5.10,29 5.2330
picolinic acidb	2,6-DHB, triazole, glycolate, acetate, 2MI	1.85c, 5.29 ± 0.38	2.16,32 5.5232	Besd	triazole, glycolate, acetate, 2MI	6.72 ± 0.34	7.03,12 7.1833	phthalic acid	triazole, glycolate, acetate, 2MI	3.48 ± 0.43, 6.07 ± 0.51	3.41,6 3.46,1 6.531
acetylacetone	IM, 2MI, DMG	9.23 ± 0.50e	9.7134	4CNf	2MI, DMG	8.25 ± 0.45	8.5635	quinineg	DMG, glycolate, acetate, IM, 2MI, DMG	3.55c, 8.35 ± 0.65	8.5436
pipecolic acid	triazole, 2MI, DMG	2.33c, 10.34 ± 0.50	2.87,32 10.4732	d-valinef	2MI, DMG	3.29c, 9.29 ± 0.47	9.6737	benzylamineh	DMG, 2MI, DMG	8.89 ± 0.69	9.2636

^aAcidic-range data set.

^b8–9 mg of 2,6-DHB.

^cApproximate pK_a1 from fitting to eq 14.

^dSample also contained DMG sodium salt (2 mM), tricine (2 mM), formate (4 mM), and tert-butylamine (10 mM), which were found unsuitable for use as indicators. A total of 5–6 mg of 2,6-DHB.

^eValue corrected for enol-ketone tautomerization.

^fSample also contained NaOH (10 mM), d-valine Na salt (2 mM), and 4CN sodium salt (20 mM).

^gBasic-range data set.

^hSample contained NaOH (10 mM) in addition to indicators. A total of 3–4 mg of 2,6-DHB.