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

Vocabulary flashcards reviewing approximate pKa values and molecular structures for select functional groups covered in Chem 0310/0320.

R Group Definition

In this pKa chart, the symbol $R$ represents an $sp^3$-hybridized carbon ($sp^3\text{-C}$) or a hydrogen atom ($H$).

Strong Mineral / Sulfonic Acids ($HX$)

Strong acids where $X = Cl, Br, I, \text{or } SO_3R$, having an approximate $p K_a$ of $-5$.

Protonated Alcohol ($R-OH_2^+$)

A protonated alcohol species (oxonium ion) with an approximate $p K_a$ of $0$.

Carboxylic Acids and Protonated Anilines

Functional group class including carboxylic acids ($R-COOH$) and protonated aniline derivatives ($Ph-NH^+(R)_2$), having an approximate $p K_a$ of $5$.

phenols, protonated amines / ammonium ions, thiols, and hydrogen cyanide

pKa of 10

Alcohol / Water ($R-OH$)

Neutral alcohols and water molecules with an approximate $p K_a$ of $15$.

Aldehyde / Ketone $\times$-Hydrogen

The acidic hydrogen on the carbon atom adjacent to a carbonyl group ($R-C(=O)-CH_2-H$), having an approximate $p K_a$ of $20$.

Terminal Alkyne ($R-C\times C-H$)

An alkyne featuring a hydrogen directly bonded to an $sp$-hybridized carbon atom, with an approximate $p K_a$ of $25$.

Neutral Amine ($R_2N-H$) and Hydrogen Gas ($H_2$)

Neutral amine species containing an $N-H$ bond and molecular hydrogen ($H-H$), with an approximate $p K_a$ of $35$.

Alkane ($R-H$)

An alkane C-H bond where $R$ is an $sp^3$-hybridized carbon atom ($R = C$), having an approximate $p K_a$ of $45$.

Carboxylic Acid ($R-COOH$)

A functional group consisting of a carbonyl group attached to a hydroxyl group, with an approximate $p K_a$ of $5$.

Anilinium Ion ($Ph-NH^+(R)_2$)

A protonated aniline species with an approximate $p K_a$ of $5$.

Phenol ($Ph-OH$)

An aromatic compound containing a hydroxyl group directly bound to a benzene ring, with an approximate $p K_a$ of $10$.

Ammonium Ion ($R_3NH^+$)

A protonated aliphatic amine with an approximate $p K_a$ of $10$.

Thiol ($R-SH$)

An organosulfur compound featuring an $S-H$ group, with an approximate $p K_a$ of $10$.

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

A linear nitrile compound with an acidic proton on the cyano carbon, having an approximate $p K_a$ of $10$.