Lecture Notes: Functional Groups and Acid-Base Concepts (pH, pKa, Ka, Kb, Henderson-Hasselbalch)

Vocabulary flashcards covering functional groups, acid-base classification, Ka/Kb, pKa/pKb, pH, and Henderson–Hasselbalch concepts.

Functional group

The reactive part of a molecule that largely determines its chemical behavior; identified first to classify a structure.

Aliphatic

Non-aromatic carbon-containing regions or chains (not part of an aromatic ring).

Aromatic

Containing an aromatic ring (such as benzene) with a conjugated pi system.

Primary alcohol

An alcohol in which the carbon bearing the OH is attached to one other carbon.

Anhydride

A functional group derived from two carboxylic acids with loss of water (R-CO-O-CO-R').

Carboxylic acid

An acidic functional group with -COOH; proton donor; commonly has a relatively low pKa (around 5).

Phenol

An -OH attached directly to an aromatic ring; weaker acid than a carboxylic acid (pKa around 10).

Amine

A nitrogen-containing base that can accept a proton; two main categories are aromatic and aliphatic based on attachment.

Aromatic amine

An amine attached to an aromatic ring; generally a weaker base (conjugate acid pKa around 5).

Aliphatic amine

An amine attached to an aliphatic (non-aromatic) carbon chain; generally a stronger base (conjugate acid pKa around 10).

Ester

A neutral functional group with a carbonyl adjacent to an -O- linkage (R-CO-O-R').

Amide

A neutral functional group (R-CO-NR2); typically not strongly acidic or basic.

Acid

A substance that donates a proton (H+) in an acid-base reaction.

Base

A substance that accepts a proton (H+) in an acid-base reaction.

Conjugate base

The species formed when an acid donates a proton; the base partner in the conjugate pair.

Conjugate acid

The species formed when a base accepts a proton; the acid partner in the conjugate pair.

Ka

The acid dissociation rate constant; larger Ka means a stronger acid.

Kb

The base dissociation rate constant; larger Kb means a stronger base.

pKa

The negative logarithm (base 10) of Ka; a fixed property of an acid indicating its strength (lower pKa = stronger acid).

pKb

The negative logarithm (base 10) of Kb; a fixed property of a base indicating its strength (higher pKb = weaker base).

pH

The negative logarithm of the hydrogen ion concentration; environment-dependent measure of acidity/basicity (0–14 under aqueous conditions).

Henderson–Hasselbalch equation

Relates pH to pKa and the ratio of conjugate base to acid: pH = pKa + log([A-]/[HA]).

Conjugate base–acid pair

Two related species in an acid–base reaction: the base (A-) with its conjugate acid (HA) after proton transfer.

Ionization

Process of forming ions by loss or gain of protons/electrons; leads to charged species and affects stability and reactions.

Zwitterion

A molecule that carries both positive and negative charges (net neutral), common for amino acids at certain pH.

Strong vs. weak acids/bases

Strong acids/bases fully ionize in solution; weak ones partially ionize, affecting pKa/pKb values.

Carboxylic acid vs. phenol acidity

Carboxylic acids are stronger acids (lower pKa, around 5) than phenols (higher pKa, around 10).