CH 18 STUDY NOTES

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Chapter 18 – Amines and Amides

Naming Amines

Amines are organic compounds derived from ammonia (NH3) by replacing one or more hydrogen atoms with alkyl groups. The naming of amines follows IUPAC rules, with the parent chain receiving the suffix "-amine."

Primary amines: One alkyl group attached to the nitrogen (e.g., methylamine, ethylamine).
Secondary amines: Two alkyl groups attached to the nitrogen (e.g., diethylamine).
Tertiary amines: Three alkyl groups attached to the nitrogen (e.g., trimethylamine).
Number the carbon chain to give the amine group the lowest possible number.
For branched amines, use "N-" to indicate substituents on the nitrogen atom (e.g., N-methyl-1-butanamine).

Example: CH3CH2NH2 is ethylamine.

N-Substituted Amines

N-substituted amines have additional alkyl groups attached to the nitrogen. The longest carbon chain is chosen as the parent, and other groups attached to the nitrogen are named as "N-alkyl" substituents.

The parent chain gets the "-amine" suffix.
Other groups on the nitrogen are indicated with "N-" (e.g., N-ethyl-N-methyl-1-propanamine).

Aromatic Amines

Aromatic amines contain the amino group attached to an aromatic ring, such as benzene. The simplest aromatic amine is aniline (C6H5NH2).

Examples: Aniline, 4-bromoaniline, N-methylaniline.
Application: Indigo dye (used in blue jeans) is made from aromatic amines.

Substituted Amines: Classification

Amines are classified based on the number of organic groups attached to the nitrogen atom.

Type	Structure	Example
Primary (1°)	RNH2	Methylamine
Secondary (2°)	R2NH	Diethylamine
Tertiary (3°)	R3N	Trimethylamine

Skeletal Structures of Amines

When drawing skeletal structures of amines, always show the hydrogens attached to the nitrogen. This is similar to the convention for alcohols.

Hydrogen Bonding in Amines

Some amines can form hydrogen bonds, which affects their physical properties such as boiling point and solubility.

Primary and secondary amines can form hydrogen bonds due to the presence of N-H bonds.
Tertiary amines cannot form hydrogen bonds with themselves because they lack N-H bonds.
Boiling point order: Primary > Secondary > Tertiary (for similar molecular weights).

Amine Solubility

Hydrogen bonding also increases the solubility of amines in water.

Primary amines are most soluble, followed by secondary, then tertiary.
As the hydrocarbon chain length increases, solubility decreases.

Amines as Bases

Amines are basic because the nitrogen atom has a lone pair of electrons that can accept a proton (H+).

In water, amines react to form ammonium ions and hydroxide ions:

When amines act as bases, they form ammonium salts (or ammonium ions).

Neutralization of Amines

When amines react with acids, they are neutralized to form ammonium salts.

Example: (methylammonium chloride)
Ammonium salts are usually solid and water-soluble.
Common ammonium salts include ammonium chlorides and bromides.

Ammonium Salts: Applications

Ammonium salts are important in medicine and pharmacology because they increase the solubility of drugs, aiding in their absorption.

Examples: Ephedrine hydrochloride (Sudafed), Diphenhydramine hydrochloride (Benadryl).

Heterocyclic Amines

Heterocyclic amines are cyclic compounds in which the ring contains at least one nitrogen atom.

Examples: Pyrrolidine, Pyrrole, Imidazole, Piperidine, Pyridine, Pyrimidine, Purine.
Many biological molecules (e.g., nucleic acids, vitamins) contain heterocyclic amines.

Alkaloids

Alkaloids are naturally occurring amines found in plants, often with pronounced physiological effects.

Examples: Nicotine, Quinine, Caffeine, Morphine, Codeine, Heroin, OxyContin.
Alkaloids are used as medicines, stimulants, and poisons.

Amides

Amides are organic compounds derived from carboxylic acids and amines. They contain a carbonyl group (C=O) attached to a nitrogen atom.

Formed by the reaction of a carboxylic acid with ammonia or an amine:

Amides are similar to esters, but with a nitrogen atom replacing the oxygen of the ester group.

Naming Amides

Amides are named by replacing the "-oic acid" or "-ic acid" ending of the parent carboxylic acid with "-amide." For N-substituted amides, the substituents on the nitrogen are indicated with "N-" prefixes.

Examples: Methanamide (formamide), Ethanamide (acetamide), Benzamide.
N,N-Dimethylbutanamide: both substituents are on the nitrogen.

Hydrolysis of Amides

Amides can be hydrolyzed (broken down) by acids or bases to yield carboxylic acids (or their salts) and amines (or ammonium ions).

Acid hydrolysis:

Base hydrolysis:

Chapter 19 Part I – Amino Acids and Proteins

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid contains an amino group (–NH2), a carboxyl group (–COOH), a hydrogen atom, and a unique side chain (R group) attached to a central (α) carbon.

There are 20 standard amino acids found in proteins.
The properties of amino acids depend on the nature of the R group.

Primary Structure of Proteins

The primary structure of a protein is the specific sequence of amino acids in a polypeptide chain, held together by peptide bonds.

Peptide bond: linkage between amino acids.
The sequence determines the protein's properties and function.

Secondary Structure of Proteins

The secondary structure refers to local folding patterns within a polypeptide, stabilized by hydrogen bonds between backbone atoms.

α-Helix: A right-handed coil with side chains projecting outward.
β-Sheet: Polypeptide chains aligned side by side in parallel or antiparallel rows.

Tertiary Structure of Proteins

The tertiary structure is the overall three-dimensional shape of a single polypeptide chain, resulting from interactions among side chains (R groups).

Stabilized by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges.

Quaternary Structure of Proteins

Some proteins consist of two or more polypeptide chains (subunits) that associate to form a functional protein. The arrangement of these subunits is the quaternary structure.

Example: Hemoglobin has four subunits (two α and two β chains).

Protein Denaturation

Denaturation is any disruption of the interactions in a protein that renders it inactive. This may cause the protein to unfold or lose its functional shape.

Denatured proteins may become insoluble or lose biological activity.

Methods of Denaturation

Changing the solvent: Organic solvents can shift hydrophobic and hydrophilic side chains, altering protein structure.
Changing the pH: Alters the ionization of acidic and basic side chains, disrupting ionic interactions.
Raising the temperature: Increases molecular motion, disrupting non-covalent interactions.
Violent agitation: Physical agitation (e.g., whipping) can denature proteins.
Adding ionic substances: High concentrations of ions or heavy metals disrupt ionic and disulfide bonds.

Summary Table: Protein Structure Levels

Level	Description	Stabilizing Forces
Primary	Sequence of amino acids	Peptide bonds
Secondary	Local folding (α-helix, β-sheet)	Hydrogen bonds
Tertiary	3D shape of polypeptide	Hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges
Quaternary	Association of multiple polypeptides	Same as tertiary

Example: Denaturation in Cooking

Egg white proteins denature and coagulate when heated, turning from clear to white and forming an insoluble tangle.

Practice Question

Which of the following amino acids can form an ion pair with glutamic acid at pH 7?

Glutamine
Glycine
Arginine (Correct: Arginine is basic and can form an ion pair with acidic glutamic acid)

Additional info: Beta sheets are very strong secondary structures and have inspired the design of synthetic polymers with high strength, such as Kevlar.

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