Table 1. Summary of ketone relaxation of non-fluorinated 1,3-dicarbonyl systems. The k_obs values for relaxation of photo-ketonized forms of 4a–d (0.025 mM) were determined in MeCN at 20 °C in the presence of additives. Percentages represent volumes of additive in MeCN. Equilibrium constants K_e were determined by NMR spectroscopy or by linear interpolation, extrapolation or averaging of the measured data. Forward and reverse rate constants, k_for(H) and k_rev(H), for enolization and ketonization processes, of the non-fluorinated 1,3-dicarbonyl systems, respectively were calculated using eqn (1) and (2).

Aryl substituent	Additive	Quantity of additive	k obs/s–1	Approx. t1/2	K e(H)	k for(H)/s–1	k rev(H)/s–1	k for(H) {with additive}/kfor(H) {MeCN}
4a (R = H)	None	—	7.26 × 10–5	2.7 h	10.5 a	6.63 × 10–5	6.31 × 10–6	1.0
	Water	15%	8.44 × 10–5	2.3 h	7.8 c	7.48 × 10–5	9.59 × 10–6	1.1
		20%	1.79 × 10–4	1.1 h	6.9 b	1.56 × 10–4	2.27 × 10–5	2.4
		25%	1.84 × 10–4	1 h	6.6 c	1.60 × 10–4	2.42 × 10–5	2.4
		35%	3.39 × 10–4	34 min	6.3 c	2.93 × 10–4	4.64 × 10–5	4.4
		50%	7.29 × 10–4	15 min	5.7 b	6.20 × 10–4	1.09 × 10–4	9.4
	Formic acid	0.5%	1.92 × 10–3	6 min	10.3 c	1.75 × 10–3	1.70 × 10–4	26
		1%	4.16 × 10–3	3 min	10.0 b	3.78 × 10–3	3.78 × 10–4	57
		2%	4.89 × 10–3	2 min	10.5 b	4.46 × 10–3	4.25 × 10–4	67
		3%	6.29 × 10–3	2 min	9.5 b	5.69 × 10–3	5.99 × 10–4	86
	DABCO	2.5 μM	2.92 × 10–3	4 min	6.7 c	2.54 × 10–3	3.80 × 10–4	39
		12.5 μM	1.34 × 10–2	1 min	6.7 c	1.17 × 10–2	1.74 × 10–3	176
		25 μM (1 eq.)	2.49 × 10–2	30 s	6.7 b	2.17 × 10–2	3.24 × 10–3	327
		37.5 μM	4.08 × 10–2	17 s	6.7 c	3.55 × 10–2	5.30 × 10–3	536
		50 μM	5.22 × 10–2	13 s	6.7 b	4.54 × 10–2	6.78 × 10–3	685
	ClCH2-DABCO+BF4–	12.5 μM	1.04 × 10–4	2 h	9.1 c	9.37 × 10–5	1.03 × 10–5	1.4
		25 μM (1 eq.)	1.20 × 10–4	1.6 h	9.1 b	1.08 × 10–4	1.19 × 10–5	1.6
		50 μM	1.32 × 10–4	1.5 h	9.1 c	1.19 × 10–4	1.31 × 10–5	1.8
		625 μM	1.00 × 10–4	2 h	9.1 c	9.01 × 10–5	9.90 × 10–6	1.4
		1.25 mM	5.12 × 10–5	4 h	9.1 c	4.61 × 10–5	5.07 × 10–6	0.7
		2.5 mM	2.04 × 10–5	9 h	9.1 c	1.84 × 10–5	2.02 × 10–6	0.3
	20% water and ClCH2-DABCO+BF4–	20%/12.5 μM	2.05 × 10–4	1 h	6.9 c	1.79 × 10–4	2.59 × 10–5	2.7
	nBu4N+BF4–	240 mM	1.44 × 10–4	1.3 h	9.1 b	1.30 × 10–4	1.43 × 10–5	2.0
4b (R = OMe)	None	—	1.29 × 10–5	15 h	4.0 a	1.03 × 10–5	2.58 × 10–6	1.0
	Water	50%	1.47 × 10–4	1.3 h	3.7 b	1.16 × 10–4	3.13 × 10–5	11
	Formic acid	2%	8.27 × 10–3	1.4 min	5.3 b	6.96 × 10–3	1.31 × 10–3	674
	DABCO	2.5 μM	8.24 × 10–4	14 min	5.1 b	6.89 × 10–4	1.35 × 10–4	67
	ClCH2-DABCO+BF4–	50 μM	7.11 × 10–6	27 h	5.0 b	5.93 × 10–6	1.19 × 10–6	0.6
4c (R = Me)	None	—	5.67 × 10–5	3.5 h	8.0 a	5.04 × 10–5	6.30 × 10–6	1.0
	Water	50%	3.15 × 10–4	37 min	8.0 d	2.80 × 10–4	3.50 × 10–5	5.6
	DABCO	2.5 μM	8.03 × 10–4	14 min	8.0 d	7.14 × 10–4	8.92 × 10–5	14
4d (R = Cl)	None	—	1.07 × 10–4	2 h	12.5 a	9.91 × 10–5	7.93 × 10–6	1.0
	Water	50%	2.13 × 10–3	5 min	12.5 d	1.97 × 10–3	1.58 × 10–4	20
	DABCO	2.5 μM	7.69 × 10–3	1.5 min	12.5 d	7.12 × 10–3	5.70 × 10–4	72
	ClCH2-DABCO+BF4–	25 μM	7.35 × 10–5	2.6 h	12.5 d	6.81 × 10–5	5.44 × 10–6	0.7

^aMeasured by ¹H NMR spectroscopy in MeCN-d₃.

^bMeasured by ¹H NMR spectroscopy in MeCN-d₃ in the presence of additive (for details see ESI Section 3.2†).

^cValue based on average of measured values or interpolation of measured values.

^d K _e(H) value was assumed to be the same as K_e(H) in MeCN-d₃ alone.