Table 2. Summary of diketone relaxation of 2-fluorinated-1,3-dicarbonyl systems. The k_obs values for relaxation of photoketonized forms of 5a–d (0.50 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(F) and k_rev(F), for enolization and ketonization processes, of the 2-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(F)	k for(F)/s–1	k rev(F)/s–1	k for(F){with additive}/kfor(F){MeCN}
5a (R = H)	None	—	— a	—	0.053 b	3.66 × 10–8 (1.58 × 10–2) c	6.91 × 10–7 (0.298) c	1.0
	Water	10%	4.98 × 10–5	4 h	0.053 d	2.49 × 10–6	4.73 × 10–5	68
		20%	1.19 × 10–4	1.6 h	0.053 d , e	5.95 × 10–6	1.13 × 10–4	163
		30%	2.23 × 10–4	0.9 h	0.053 d	1.12 × 10–5	2.12 × 10–4	305
		40%	3.77 × 10–4	0.5 h	0.053 d	1.89 × 10–5	3.58 × 10–4	515
		50%	6.78 × 10–4	0.3 h	0.053 b	3.39 × 10–5	6.44 × 10–4	926
	Formic acid	3%	1.64 × 10–4	1.2 h	0.053 b	8.20 × 10–6	1.56 × 10–4	224
	DABCO	2.5 μM	1.42 × 10–3	8 min	— f	— f	— f	— f
	ClCH2-DABCO+BF4–	12.5 μM	1.01 × 10–6	8 d	0.053 d	5.05 × 10–8	9.60 × 10–7	1.4
		25 μM (1 eq.)	2.93 × 10–6	2.7 d	0.053 d	1.47 × 10–7	2.78 × 10–6	4.0
	20% water and ClCH2-DABCO+BF4–	20%/12.5 μM	1.91 × 10–4	1 h	0.053 d	9.55 × 10–6	1.81 × 10–4	261
	nBu4N+BF4–	240 mM	8.38 × 10–5	2.3 h	0.043 g	3.42 × 10–6	8.04 × 10–5	94
5b (R = OMe)	None	—	1.46 × 10–7 h	60 d	0.020 b	2.92 × 10–9 (n.d.) c	1.43 × 10–7 (n.d.) c	1.0
	Water	20%	3.22 × 10–5	6 h	0.033 d	1.04 × 10–6	3.12 × 10–5	355
		30%	5.39 × 10–5	3.6 h	0.040 d	2.06 × 10–6	5.18 × 10–5	706
		40%	9.23 × 10–5	2.1 h	0.046 d	4.07 × 10–6	8.82 × 10–5	1396
		50%	1.71 × 10–4	1.1 h	0.053 b	8.55 × 10–6	1.62 × 10–4	2928
	Formic acid	2%	1.73 × 10–5	11 h	0.031 b	5.19 × 10–7	1.68 × 10–5	178
	DABCO	2.5 μM	1.32 × 10–5	15 h	0.020 b	2.64 × 10–7	1.29 × 10–5	90
5c (R = Me)	None	—	8.64 × 10–8 h	90 d	0.149 b	1.12 × 10–8	7.52 × 10–8	1.0
	Water	50%	9.15 × 10–4	0.2 h	0.149 i	1.19 × 10–4	7.96 × 10–4	10 594
5d (R = Cl)	None	—	— a	—	0.087 b	5.37 × 10–8 (1.11 × 10–2) c	6.18 × 10–7 (0.128) c	1.0
	Water	50%	1.97 × 10–3	6 min	0.087 i	1.58 × 10–4	1.81 × 10–3	2936

^aSystem displayed non-first order autocatalytic behaviour.

^bMeasured by ¹⁹F NMR spectroscopy in MeCN-d₃ or MeCN-d₃/D₂O.

^cSecond order rate constant for autocatalytic process in units of M^–1 s^–1.

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

^eA ¹⁹F NMR spectroscopy measurement in 20% H₂O/MeCN-d₃ gave K_e(F) = 0.042.

^fDefluorination was observed.

^gMeasured in the presence of 300 mM ⁿBu₄N⁺BF₄^–.

^hExtremely slow process, where rate constant was determined by initial rates method.

ⁱ K _e(F) for 50% H₂O was assumed to be the same as K_e(F) in MeCN-d₃.