What functional groups can act as acids?

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Answer 1 · 2014-02-19T16:28:41

The sulfonic, phosphoric, and carboxylic acid groups are the strongest acids. Many functional groups behave as weaker acids.

A functional group is an acid if it can donate a proton to a base.

Here is a list of functional groups that can behave as acids, along with their approximate #pK_a# values.

R-SO₃H — sulfonic acids — #pK_a# = -1 (important in industry)

R-PO₄H₂ — phosphoric acids — #pK_a# = 2 (important in biochemistry)

R-COOH — carboxylic acids — #pK_a# = 4

R-SH — Thiols — #pK_a# = 13

R-OH — Alcohols — #pK_a# = 17

R-NH₂ — Amines — #pK_a# = 35

C-H bonds can also behave as acids. Their #pK_a# values range from 13 to 50, depending on the groups that are next to the C atom.