General Chemistry Study Guide: Lipids, Fatty Acids, and Amines/Amides

Chapter 17: Lipids and Fatty Acids

Hydrophilic vs. Hydrophobic & Solubility of Fatty Acids

Fatty acids are amphipathic molecules, meaning they contain both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. This dual nature affects their solubility in water and their biological functions.

• Hydrophilic region: The carboxylic acid group (-COOH) interacts with water.

• Hydrophobic region: The long hydrocarbon chain repels water.

• Solubility: Short-chain fatty acids are more soluble in water than long-chain fatty acids due to the relative size of the hydrophilic group.

• Example: Stearic acid (C18H36O2) is largely insoluble in water.

Functions of Lipids

Lipids serve several essential roles in biological systems.

• Energy storage: Triglycerides store energy efficiently.

• Structural components: Phospholipids form cell membranes.

• Signaling molecules: Steroids and eicosanoids act as hormones and messengers.

Facts about Fatty Acids and Structure of Fatty Acids

Fatty acids are carboxylic acids with long hydrocarbon chains. They can be saturated or unsaturated.

• Saturated fatty acids: No double bonds; straight chains (e.g., palmitic acid).

• Unsaturated fatty acids: One or more double bonds; kinked chains (e.g., oleic acid).

• General formula: $\mathrm{CH_3(CH_2)_nCOOH}$

Saturated vs. Unsaturated Fatty Acids

The presence or absence of double bonds in fatty acids affects their physical properties and biological roles.

• Saturated: Solid at room temperature; found in animal fats.

• Unsaturated: Liquid at room temperature; found in plant oils.

• Example: Butter (saturated) vs. olive oil (unsaturated).

The Role of Enzymes in Fatty Acid Synthesis and Hydrolysis

Enzymes catalyze both the synthesis and breakdown of fatty acids.

• Synthesis: Fatty acid synthase builds fatty acids from acetyl-CoA.

• Hydrolysis: Lipases break down triglycerides into fatty acids and glycerol.

NSAIDs and Eicosanoids

Eicosanoids are signaling molecules derived from fatty acids. NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) inhibit enzymes involved in eicosanoid synthesis.

• Role: Eicosanoids regulate inflammation, immunity, and other functions.

• NSAIDs: Block cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis.

Lipoproteins: LDL, HDL, Cholesterol Transport

Lipoproteins are complexes that transport lipids in the blood.

• LDL (Low-Density Lipoprotein): Delivers cholesterol to cells; high levels linked to heart disease.

• HDL (High-Density Lipoprotein): Removes cholesterol from cells; protective effect.

• Packaging and transport: Lipids are packaged into lipoproteins for movement through the bloodstream.

Steroids

Steroids are a class of lipids with a characteristic four-ring structure.

• Examples: Cholesterol, testosterone, estrogen.

• Functions: Hormonal regulation, membrane structure.

Cell Membranes

Cell membranes are primarily composed of phospholipids, cholesterol, and proteins.

• Phospholipid bilayer: Provides structural integrity and selective permeability.

• Cholesterol: Modulates fluidity and stability.

Chapter 18: Amines and Amides

Classification and Naming of Amines (1°, 2°, 3°)

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

• Primary (1°) amine: One alkyl/aryl group attached to nitrogen (e.g., methylamine).

• Secondary (2°) amine: Two alkyl/aryl groups (e.g., dimethylamine).

• Tertiary (3°) amine: Three alkyl/aryl groups (e.g., trimethylamine).

• Naming: Use the names of attached groups followed by "amine" (e.g., ethylmethylamine).

Properties of Amines and Amides

Amines and amides have distinct physical and chemical properties.

• Amines: Basic, can form hydrogen bonds, moderate boiling points.

• Amides: Less basic, strong hydrogen bonding, higher boiling points.

• Example: Acetamide has a higher boiling point than methylamine.

Acid-Base Properties of Amines and Amides

Amines act as bases due to the lone pair on nitrogen; amides are much less basic.

• Amines: Accept protons to form ammonium ions.

• Amides: Resonance reduces basicity; less likely to accept protons.

• Equation: $\mathrm{RNH_2 + H^+ \rightarrow RNH_3^+}$

Physical Properties: Boiling Points, Polarity, and Forces

The physical properties of amines and amides are influenced by molecular structure and intermolecular forces.

• Boiling points: Amides > amines > hydrocarbons (due to hydrogen bonding).

• Polarity: Both are polar; amides are more polar due to the carbonyl group.

• Intermolecular forces: Hydrogen bonding is significant in both, especially amides.

Reactions of Amines and Amides

Amines and amides participate in various chemical reactions.

• Amines: Alkylation, acylation, reaction with acids to form salts.

• Amides: Hydrolysis (acidic or basic conditions) to yield carboxylic acids and amines.

• Equation (Amide hydrolysis): $\mathrm{RCONH_2 + H_2O \rightarrow RCOOH + NH_3}$

Table: Comparison of Amines and Amides

Property	Amines	Amides
Basicity	High	Low
Hydrogen Bonding	Moderate	Strong
Boiling Point	Moderate	High
Reactivity	Alkylation, acylation	Hydrolysis