Ordered from strongest acid to weakest.

Compound	Acidic Site	pKa (approx.)	Compound Class
HCl	H–Cl	−7	Mineral acid (reference point)
H₃O⁺	H–OH₂⁺	−1.7	Hydronium (reference point)
Trifluoroacetic acid	CF₃COOH	0.2	Carboxylic acid (heavily inductive)
Trichloroacetic acid	CCl₃COOH	0.7	Carboxylic acid (heavily inductive)
Dichloroacetic acid	Cl₂CHCOOH	1.3	Carboxylic acid
Chloroacetic acid	ClCH₂COOH	2.9	Carboxylic acid
Formic acid	HCOOH	3.8	Carboxylic acid
Benzoic acid	PhCOOH	4.2	Carboxylic acid
Anilinium ion	PhNH₃⁺	4.6	Ammonium (conjugate acid of a weak amine)
Acetic acid	CH₃COOH	4.8	Carboxylic acid
Pyridinium ion	C₅H₅NH⁺	5.2	Ammonium (aromatic amine)
p-Nitrophenol	4-O₂N–C₆H₄OH	7.2	Phenol (electron-poor ring)
Acetylacetone (pentane-2,4-dione)	–CH₂– between two C=O	~9	1,3-Dicarbonyl (doubly activated α-C–H)
Ammonium ion	NH₄⁺	9.25	Ammonium
Phenol	C₆H₅OH	10.0	Phenol
Methylammonium ion	CH₃NH₃⁺	10.6	Ammonium (alkyl amine)
Diethyl malonate	–CH₂– between two esters	~13	1,3-Dicarbonyl (doubly activated α-C–H)
Water	H₂O	15.7	Reference solvent
Ethanol	CH₃CH₂OH	16	Alcohol
tert-Butanol	(CH₃)₃COH	18	Alcohol (more hindered/less stabilized)
Acetone	CH₃–CO–CH₃, α-C–H	20	Ketone α-carbon
Terminal alkyne	HC≡CH, C–H	25	Hydrocarbon (sp C–H)
Ethyl acetate	CH₃CO–OEt, α-C–H	25	Ester α-carbon
Ammonia	NH₃	38	Reference (as an acid, not a base)
Ethylene	H₂C=CH₂, C–H	44	Hydrocarbon (sp² C–H)
Ethane	CH₃CH₃, C–H	50	Hydrocarbon (sp³ C–H)

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