pKa values and gas-phase acidities of superacid molecul
pKa values and gas-phase acidities of superacid molecul
pKa values and gas-phase acidities of superacid molecul
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Self-consistent acidity<br />
scale in MeCN<br />
Acid pK a (AN) a Directly measured ΔpK a b<br />
1 9-C 6F 5-Fluorene 28.11<br />
2 (4-Me-C 6F 4)(C 6H 5)CHCN 26.96<br />
3 (4-NC 5F 4)(C 6H 5)NH 26.34<br />
4 (C 6H 5)(C 6F 5)CHCN 26.14<br />
5 (4-Me 2N-C 6F 4)(C 6F 5)NH 25.12<br />
6 (4-Me-C 6F 4)(C 6F 5)NH 24.94<br />
7 Octafluor<strong>of</strong>luorene 24.49<br />
8 Fluoradene 23.90<br />
9 9-COOMe-Fluorene 23.53<br />
10 Acetic acid 23.51<br />
11 (C 6F 5)CH(COOEt) 2 22.85<br />
12 2-NO 2-Phenol 22.85<br />
13 (4-Me-C 6F 4) 2CHCN 22.80<br />
14 (4-Me-C 6F 4)(C 6F 5)CHCN 21.94<br />
15 Benzoic acid 21.51<br />
16 9-CN-Fluorene 21.36<br />
17 (4-H-C 6F 4)(C 6F 5)CHCN 21.11<br />
18 (C 6F 5) 2CHCN 21.10<br />
19 (CF 3) 3COH 20.55<br />
20 (4-Cl-C 6F 4)(C 6F 5)CHCN 20.36<br />
21 2,4,6-Br 3-Phenol 20.35<br />
22 (2,4,6-Cl 3-C 6F 2)(C 6F 5)CHCN 20.13<br />
23 2,3,5,6-F 4-Phenol 20.12<br />
24 2,3,4,5,6-F 5-Phenol 20.11<br />
25 (2-C 10F 7)(C 6F 5)CHCN 20.08<br />
26 1-C 10F 7OH 19.72<br />
27 2,4,6-(SO 2F) 3-Aniline 19.66<br />
28 (2-C 10F 7) 2CHCN 19.32<br />
29 9-C 6F 5-Octafluor<strong>of</strong>luorene 18.88<br />
30 2-C 10F 7OH 18.50<br />
31 (4-CF 3-C 6F 4)(C 6F 5)CHCN 18.14<br />
32 4-C 6F 5-2,3,5,6-F 4-Phenol 18.11<br />
33 (4-H-C 6F 4)CH(CN)COOEt 18.08<br />
34 2,3,4,5,6-Cl 5-Phenol 18.02<br />
35 2,3,4,5,6-Br 5-Phenol 17.83<br />
36 (C 6F 5)CH(CN)COOEt 17.75<br />
37 4-Me-C 6H 4CH(CN) 2 17.59<br />
38 (2-C 10F 7)CH(CN)COOEt 17.50<br />
39 (4-Cl-C 6F 4)CH(CN)COOEt 17.39<br />
40 2,4-(NO 2) 2-Phenol 16.66<br />
41 4-CF 3-2,3,5,6-F 4-Phenol 16.62<br />
42 (4-NC 5F 4)(C 6F 5)CHCN 16.40<br />
43 (4-CF 3-C 6F 4) 2CHCN 16.13<br />
44 (4-CF 3-C 6F 4)CH(CN)COOEt 16.08<br />
45 (4-NC 5F 4)(2-C 10F 7)CHCN 16.02<br />
46 4-NC 5F 4-OH 15.40<br />
47 (4-NC 5F 4)CH(CN)COOEt 14.90<br />
1.15<br />
0.63<br />
0.20<br />
1.03<br />
0.64<br />
0.96<br />
0.67<br />
0.90<br />
0.60<br />
1.01<br />
0.21<br />
0.42<br />
0.40<br />
0.44<br />
0.38<br />
0.36<br />
0.06<br />
0.59<br />
1.49<br />
1.32<br />
1.96<br />
1.20<br />
0.45<br />
0.58<br />
1.05<br />
0.92<br />
0.42<br />
0.39<br />
1.02<br />
0.01<br />
0.43<br />
0.34<br />
1.19<br />
0.75<br />
0.77<br />
0.22<br />
0.32<br />
0.06<br />
1.12<br />
019<br />
1.78<br />
0.17<br />
-0.01<br />
1.49<br />
0.25<br />
0.76<br />
0.81<br />
0.79<br />
0.46<br />
0.19<br />
0.08<br />
1.10<br />
0.60<br />
1.35<br />
0.82<br />
0.68<br />
0.04<br />
0.26<br />
0.53<br />
0.26<br />
0.03<br />
0.03<br />
0.85<br />
0.73<br />
0.04<br />
1.15<br />
0.54<br />
1.43<br />
0.73<br />
0.75<br />
0.71<br />
0.48 1.02<br />
0.41<br />
0.92<br />
1.92<br />
1.59<br />
0.10<br />
0.27<br />
0.27<br />
0.05<br />
0.70<br />
0.69<br />
1.75<br />
1.70<br />
1.51<br />
1.21<br />
0.63<br />
0.88<br />
0.37<br />
-0.01<br />
0.82<br />
1.46<br />
0.72<br />
1.03<br />
0.26<br />
1.02<br />
0.28<br />
0.29<br />
0.25<br />
0.00<br />
0.80<br />
0.06<br />
1.32<br />
47 (4-NC 5F 4)CH(CN)COOEt 14.90<br />
0.69<br />
0.19<br />
48 3-CF 3-C 6H 4CH(CN) 2 14.72<br />
0.15<br />
49 Saccharin 14.57 0.84<br />
0.71<br />
1.89<br />
50 4-Me-C 6F 4CH(CN) 2 13.87<br />
0.40<br />
51 (4-NC 5F 4) 2CHCN 13.46<br />
0.87<br />
0.45 0.89<br />
52 C 6F 5CH(CN) 2 13.01<br />
0.48<br />
0.03 0.04<br />
53 4-H-C 6F 4CH(CN) 2 12.98<br />
0.79<br />
0.74<br />
54 2-C 10F 7CH(CN) 2 12.23<br />
1.38 0.26<br />
55 Tos 2NH c 11.97 0.62<br />
56 4-NO 2-C 6H 4CH(CN) 2 11.61<br />
0.03<br />
57 4-MeO-C 6H 4C(=O)NHTf d 11.60<br />
0.28<br />
0.19 0.14<br />
58 4-Me-C 6H 4C(=O)NHTf 11.46<br />
1.21<br />
0.98<br />
59 (C 6H 5SO 2) 2NH 11.34 0.60<br />
0.60<br />
0.57<br />
60 4-Cl-C 6H 4SO 2NHTos 11.10<br />
0.49<br />
0.36<br />
61 C 6H 5C(=O)NHTf 11.06<br />
1.43<br />
0.10<br />
0.07<br />
62 Picric acid 11.00<br />
63 4-F-C 6H 4C(=O)NHTf 10.65<br />
0.91<br />
0.79<br />
0.87<br />
64 4-Cl-C 6H 4C(=O)NHTf 10.36 0.82<br />
0.54<br />
65 (4-Cl-C 6H 4SO 2) 2NH 10.20<br />
0.15<br />
0.56<br />
-0.01<br />
66 4-CF 3-C 6F 4CH(CN) 2 10.19<br />
0.13<br />
1.15<br />
0.14<br />
67 4-NO 2-C 6H 4SO 2NHTos 10.04 0.52<br />
1.20<br />
1.06<br />
0.73<br />
68 4-Cl-3-NO 2-C 6H 3SO 2NHTos 9.71 1.05 0.46<br />
69 4-NO 2-C 6H 4C(=O)NHTf 9.49 0.53<br />
0.23<br />
70 4-NO 2-C 6H 4SO 2NHSO 2C 6H 4-4-Cl 9.17<br />
2.3<br />
0.56 1.73<br />
71 TosOH 8.6<br />
1.21 0.23<br />
72 (4-NO 2-C 6H 4SO 2) 2NH 8.32<br />
1.3<br />
0.25<br />
73 1-C 10H 7SO 3H 8.02<br />
0.50<br />
0.19 1.04<br />
74 C 6H 5CHTf 2 7.85<br />
0.54 1.25<br />
75 4-Cl-C 6H 4SO 3H 7.3<br />
0.53<br />
76 3-NO 2-C 6H 4SO 3H 6.78 0.51<br />
77 4-NO 2-C 6H 4SO 3H 6.73<br />
78 4-MeO-C 6H 4C(=NTf)NHTf 6.54 0.51<br />
0.44 1.28 0.23<br />
79 4-Me-C 6H 4C(=NTf)NHTf 6.32<br />
0.75 0.23<br />
0.05<br />
0.62<br />
80 TosNHTf 6.30<br />
0.5<br />
0.16 0.35<br />
81 C 6H 5C(=NTf)NHTf 6.17 0.36<br />
1.11 0.47<br />
82 C 6H 5SO 2NHTf 6.02<br />
0.59<br />
0.26<br />
83 4-F-C 6H 4C(=NTf)NHTf 5.79 0.83<br />
1.64<br />
84 4-Cl-C 6H 4C(=NTf)NHTf 5.69<br />
0.77<br />
1.37<br />
85 2,4,6-(SO 2F) 3-Phenol 5.66<br />
1.25<br />
0.64<br />
86 4-Cl-C 6H 4SO 2NHTf 5.47<br />
0.42<br />
0.59<br />
0.71<br />
87 4-Cl-C 6H 4SO(=NTf)NHTos 5.27<br />
0.53<br />
88 4-NO 2-C 6H 4C(=NTf)NHTf 5.13 0.38<br />
1.20<br />
89 2,4,6-Tf 3-Phenol 4.93<br />
0.41<br />
1.1<br />
90 4-NO 2-C 6H 4SO 2NHTf 4.52<br />
0.05<br />
0.87<br />
91 4-Cl-C 6H 4SO(=NTf)NHSO 2C 6H 4-4-Cl 4.47 1.10 1.15<br />
0.31<br />
92 2,3,5-tricyanocyclopentadiene 4.16<br />
0.74<br />
0.50<br />
93 4-Cl-C 6H 4SO(=NTf)NHSO 2C 6H 4-4-NO 2 3.75<br />
A. Kütt et al, J. Org. Chem. 2006, 71, 2829<br />
17<br />
A. Kütt et al, J. Org. Chem. 2011, 76, 391<br />
Properties <strong>of</strong> the MeCN acidity scale<br />
• Consistency, checked by circular<br />
validation measurements:<br />
• 93 acids, 203 relative acidity measurements<br />
• Consistency st<strong>and</strong>ard deviation: 0.03 pK a<br />
units<br />
• Anchored to Picric acid (pK a = 11.0)<br />
• pK a range: 3.7 .. 28.1<br />
• Useful tool for further studies<br />
• Acids in the lower part are <strong>superacid</strong>s<br />
• pK a<br />
(H 2<br />
SO 4<br />
) ≈ 8 in MeCN<br />
18<br />
9