Carboxylic Acids

Structure and Properties

Carboxylic acids are organic compounds containing a carbonyl group (C=O) bonded to a hydroxyl group (–OH). The general formula is R–COOH, where R is a carbon-containing group. Carboxylic acids are more oxidized than aldehydes and ketones.

• Intermolecular forces: Carboxylic acids form hydrogen bonds, acting as both donors and acceptors.

• Solubility: Usually water-soluble unless the carboxyl group is a small percentage of the molecule's mass (e.g., fatty acids).

• Acidity: Carboxylic acids are weak acids, with typical pKa values around 3–4. They can donate a proton to water.

Example: Acetic acid (CH3COOH) is a common carboxylic acid.

Carboxylate Salts

Carboxylate salts are formed by the neutralization of carboxylic acids with metal hydroxides. They are ionic and more water-soluble than their parent acids.

• Reaction:

• Properties: Ionic interactions replace hydrogen bonding, increasing solubility (e.g., soaps).

Condensation Reactions

Carboxylic acids undergo condensation reactions to form esters and amides.

• Esterification:

• Amide formation:

Esters

Structure and Properties

Esters are derived from carboxylic acids and alcohols. They have the general formula R–COOR'.

• Intermolecular forces: Esters use dipole-dipole interactions and are hydrogen bond acceptors, but not donors.

• Solubility: Esters can hydrogen bond with water, but have weaker IMFs than carboxylic acids (more volatile, lower boiling point).

Reactions

• Esterification: Formation from carboxylic acids and alcohols.

• Hydrolysis: Esters can be hydrolyzed by water or base (saponification) to yield carboxylic acids or carboxylate salts.

• Saponification:

Example: Triacylglycerols (triglycerides) are esters formed from fatty acids and glycerol.

Amines

Structure and Classification

Amines are derivatives of ammonia (NH3) with one or more hydrogen atoms replaced by carbon groups. They are classified as primary (1°), secondary (2°), tertiary (3°), or quaternary (4°) based on the number of carbon groups attached to nitrogen.

• Primary amine: R–NH2

• Secondary amine: R2–NH

• Tertiary amine: R3–N

• Quaternary ammonium: R4–N+

Properties

• Intermolecular forces: 1° and 2° amines can hydrogen bond (donor and acceptor), 3° amines only accept hydrogen bonds (dipole-dipole interactions).

• Solubility: Usually water-soluble unless a large hydrophobic group is present.

• Odor: Many amines have strong odors (e.g., putrescine, cadaverine).

Basicity and Amine Salts

• Basicity: Amines act as weak bases, accepting protons.

• Amine salts: Formed by reaction with acids, resulting in charged, water-soluble ions.

• Reaction:

Biological Examples

• Amino acids: Basic amino acids (e.g., lysine) contain amines.

• Nucleotides: DNA/RNA bases contain heterocyclic amines.

• Drugs: Many drugs are amine salts for increased solubility (e.g., fluoxetine-HCl).

Amides

Structure and Formation

Amides are formed from the reaction of carboxylic acids and amines. The general formula is R–CONHR'.

• Classification: Primary, secondary, and tertiary amides based on the number of carbon groups attached to nitrogen.

• Formation:

Properties

• Intermolecular forces: 1° and 2° amides can hydrogen bond; 3° amides use dipole-dipole interactions.

• Solubility: Usually water-soluble unless a large hydrophobic group is present.

• Basicity: Amides are not basic; the nitrogen lone pair is attracted to the carbonyl carbon.

Biological Example: Peptide Bonds

Proteins are synthesized by linking amino acids via amide bonds, called peptide bonds.

Hydrolysis of Amides

• Acid hydrolysis: Produces amine salt.

• Base hydrolysis: Produces carboxylate salt.

Thiols and Thioesters

Thiols

Thiols are similar to alcohols, but contain sulfur instead of oxygen. The general formula is R–SH.

• Properties: Dipole-dipole interactions, do not form hydrogen bonds, less polar than alcohols, more reactive.

• Odor: Characteristic "skunky" smell; used as odorant in natural gas.

Disulfide Formation

Thiols can be oxidized to form disulfides, a reversible reaction important in protein structure.

• Reaction:

Thioesters

Thioesters are similar to esters, but contain sulfur in place of the single-bonded oxygen. They are formed from carboxylic acids and thiols.

• Biological importance: Thioesters (e.g., acetyl-CoA) are high-energy compounds used in metabolism.

Phosphate Compounds

Phosphoesters and Phosphoanhydrides

Phosphate compounds are essential in biochemistry. Phosphoesters contain a C–O–P bond, while phosphoanhydrides contain a P–O–P bond.

• Phosphoester: Formed from reaction of phosphate with alcohol.

• Phosphoanhydride: Formed from reaction of two phosphates, eliminating water.

ATP and Energy

ATP (adenosine triphosphate) contains phosphoanhydride bonds. Breaking these bonds releases energy for cellular processes.

• Hydrolysis:

• Phosphorylation: Transfer of phosphate from ATP to another molecule (e.g., glucose in glycolysis).

Summary Table: Carbonyl-Containing Groups

Additional info: These notes cover the structure, properties, and reactions of carboxylic acids, esters, amines, amides, thiols, thioesters, and phosphate compounds, as relevant to GOB Chemistry. Biological examples and applications are included for context.