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Table 2 Rankings (smallest numbers indicating most acidic) and SMARTS strings to identify acid and base substructures for competitive ionization of molecules based on FDA 2007

From: The Chemical Validation and Standardization Platform (CVSP): large-scale automated validation of chemical structure datasets

Group Acid SMARTS Conjugated Base SMARTS Rank
OSO3H OS(=O)(=O)[O;H] OS(=O)(=O)[O-] 10
SO3H [!O]S(=O)(=O)[O;H] [!O]S(=O)(=O)[O-] 20
OSO2H O[S;D3](=O)[O;H] O[S;D3](=O)[O-] 30
SO2H [!O][S;D3](=O)[O;H] [!O][S;D3](=O)[O-] 40
OPO3H2 OP(=O)([O;H])[O;H] OP(=O)([O;H])[O-] 50
PO3H2 [!O]P(=O)([O;H])[O;H] [!O]P(=O)([O;H])[O-] 60
CO2H C(=O)[O;H] C(=O)[O-] 70
Arom-SH c[S;H] c[S-] 80
OPO3H- OP(=O)([O;H])[O-] OP(=O)([O-])[O-] 90
PO3H [!O]P(=O)([O;H])[O-] [!O]P(=O)([O-])[O-] 100
Phthalimide O = C2c1ccccc1C(=O)[N;H]2 O = C2c1ccccc1C(=O)[N-]2 110
CO3H C(=O)O[O;H] C(=O)O[O-] 120
α-carbon to NO2 group O = N(O)[C;H] O = N(O)[C-] 130
SO2NH2 S(=O)(=O)[NH2] S(=O)(=O)[NH-] 140
OB(OH)2 OB([OH])[OH] OB([OH])[O-] 150
B(OH)2 [!O]B([OH])[OH] [!O]B([OH])[O-] 160
Arom-OH c[OH] c[O-] 170
SH aliphatic C[SH] C[S-] 180
OBO2H OB([OH])[O-] OB([O-])[O-] 190
BO2H [!O]B([OH])[O-] [!O]B([O-])[O-] 200
Cyclopentadiene [CH2]1C = CC = C1 [C-]1C = CC = C1 210
Amide C(=O)[NH2 C(=O)[N;H;-] 220
Imidazole c1cnc[n]1 c1cnc[n-]1 230
Aliphatic OH [CX4][OH] [CX4][O-] 240
H at α-carbon to carboxyl O = C[CH] O = C[C-] 250
H at α-carbon to acetyl OC(=O)[CH] OC(=O)[C-] 260
H at sp carbon C#[CH] C#[C-] 270
H at α -carbon of sulfone group CS(=O)(=O)C[CH] CS(=O)(=O)C[C-] 280
H at α-carbon of sulfoxide C[S;D3](=O)C[CH] C[S;D3](=O)C[C-] 290
Amine [CX4][NH2] [CX4][N;H;-] 300
Benzyl c[C;D4;H] c[C;D3;-] 310
H at sp2 carbon [CX3;H] [CX3;-] 320
H at sp3 carbon [CX4;H] [CX3-] 330