Chem 0310/0320: Approximate pKa Values for Select Functional Groups

Vocabulary flashcards detailing functional groups and their approximate pKa values from strongest to weakest acids.

R Group (in pKa chart context)

Defined specifically as an $sp^3\text{-C}$ or $H$.

Acidic Hydrogen Representation

The specific hydrogen atom(s) drawn explicitly with the letter $H$ to designate the proton associated with the given $pK_a$ value.

$H-X$ ($X = Cl, Br, I$, or $SO_3R$)

Strongest acids on the chart, characterized by an approximate $pK_a$ value of $-5$.

Protonated Oxygen / Hydronium Species

Protonated molecule bearing an acidic hydrogen on a positively charged oxygen, having an approximate $pK_a$ value of $0$.

Carboxylic Acid

Functional group containing a carbonyl bonded to a hydroxyl group ($R-COOH$), with an approximate $pK_a$ value of $5$.

Thiol ($R-S-H$)

Sulfur-containing functional group with an acidic hydrogen, having an approximate $pK_a$ value of $10$.

Hydrogen Cyanide ($H-C\equiv N$)

Nitrile compound with a terminal acidic hydrogen, having an approximate $pK_a$ value of $10$.

Alcohol ($R-O-H$) and Water ($H-O-H$)

Neutral oxygen-containing functional groups with an $O-H$ bond, having an approximate $pK_a$ value of $15$.

Ketone ($\alpha$-hydrogen)

Carbonyl compound with an acidic hydrogen located on the adjacent carbon, having an approximate $pK_a$ value of $20$.

Terminal Alkyne

Hydrocarbon containing a carbon-carbon triple bond with an acidic hydrogen ($C\equiv C-H$), having an approximate $pK_a$ value of $25$.

Amine ($R_2N-H$) and Molecular Hydrogen ($H-H$)

Nitrogen-containing compounds with an $N-H$ bond and diatomic hydrogen, having an approximate $pK_a$ value of $35$.

Benzene Ring and Alkane ($R-H$)

Weakest acids on the chart, consisting of aromatic ring hydrogens and aliphatic $C-H$ bonds ($R = C$), having an approximate $pK_a$ value of $45$.