. Author manuscript; available in PMC: 2012 Mar 9.

Published in final edited form as: J Am Chem Soc. 2011 Feb 16;133(9):3173–3183. doi: 10.1021/ja110795m

Table 3.

Rate Constants for Exchange of the First α-Proton of Glycine in the Presence of 3 and HFIP Buffers in D₂O^a

Base	f_B^c	pD	[aldehyde]/M	f_3-IM-D^d	k_o/s⁻¹^e	k_w/s⁻¹^f	(k_buf)_obsd/M⁻¹s⁻¹^g	k_B/M⁻¹s⁻¹^h
HFIP	0.8	10.53	6.0 × 10⁻³	0.15	1.7 × 10⁻⁶	1.1 × 10⁻⁵	3.1 × 10⁻⁶	2.6 × 10⁻⁵
HFIP	0.8	10.52	2.0 × 10⁻²	0.39	4.4 × 10⁻⁶	1.1 × 10⁻⁵	8.8 × 10⁻⁶	2.8 × 10⁻⁵
pK_BD = 9.9^b
	0.5	9.80	1.0 × 10⁻²	0.32	6.9 × 10⁻⁷	2.2 × 10⁻⁶	4.2 × 10⁻⁶	2.6 × 10⁻⁵
	0.5	9.86	5.2 × 10⁻²	0.73	1.8 × 10⁻⁶	2.5 × 10⁻⁶	1.2 × 10⁻⁵	3.3 × 10⁻⁵
	0.2	9.35	2.0 × 10⁻²	0.45	3.5 × 10⁻⁷	7.8 × 10⁻⁷	2.9 × 10⁻⁶	3.2 × 10⁻⁵

At 25 °C and I = 1.0 (KCl).

Apparent pK_a of the conjugate acid in D₂O at 25 °C and I = 1.0 (KCl).

Fraction of the buffer present in the basic form.

Fraction of glycine present as the reactive iminium ion 3-IM-D at the given concentration of 3, determined by ¹H NMR analysis of an equilibrium mixture of glycine and the imine.

The intercept of plots of k_ex against [buffer]_T (Figure 5).

Apparent first-order rate constants for solvent-catalyzed deprotonation of 3-IM-D, calculated from the values of k_o as described in the text.

The slope of plots of k_ex against [buffer]_T (Figure 5).

Second-order rate constants for HFIP base-catalyzed deprotonation of 3-IM-D, calculated from the values of (k_buf)_obsd as described in the text.