Table 1.

Equilibrium Constants in D₂O for Addition of Glycine to the Aromatic Aldehydes 1–4.^a

aldehyde	iminium ion	p(Ka)IMb	p(Ka)ODc	(Kadd) d (M−1)	(Kadd)+e (M−1)	(Kadd)++f (M−1)
		6.29 ± 0.01		44 ± 8	(3.3 ± 0.4) × 10−3
		12.13 ± 0.05	5.55 ± 0.04	1.76 ± 0.02	72 ± 8	(3.4 ± 0.1) × 10−2
		10.16 ± 0.03	6.61 ± 0.02	0.49 ± 0.03	0.29 ± 0.03	(8.7 ± 0.9) × 10−3
		4.95 ± 0.06		(500 ± 20)	(2.0 ± 0.4) × 10−3

^aAt 25 °C and I = 1.0 (KCl).

^bApparent pK_a of the iminium ion nitrogen in D₂O, determined by NMR titration as described in the text.

^cApparent pK_a of the iminium ion phenol group in D₂O, determined by NMR titration as described in the text.

^dEquilibrium constant for addition of the basic amino form of the amino acid to the basic form of the aldehyde.

^eEquilibrium constant for addition of the amino acid zwitterion to the basic form of the aldehyde.

^fEquilibrium constant for addition of the amino acid zwitterion to the protonated form of the aldehyde.