Structures and Properties of Fatty Acids

What are Fatty Acids? Fatty acids are carboxylic acids with a long hydrocarbon chain. They are the building blocks of lipids and play a crucial role in energy metabolism, cell membrane formation, and signaling pathways.

Structure of Fatty Acids: Fatty acids have a general structure:

R–COOH
Where:

• R = Hydrocarbon (alkyl) chain (hydrophobic, non-polar)
• COOH = Carboxyl (-COOH) functional group (hydrophilic, polar)

Parts of a Fatty Acid

1. Hydrophobic Tail → Long-chain hydrocarbon (non-polar, repels water)
2. Hydrophilic Head → Carboxyl (-COOH) group (polar, interacts with water)

Example:

• Palmitic acid (C16:0) → CH3-(CH2)14-COOH
• Oleic acid (C18:1) → CH3-(CH2)7-CH=CH-(CH2)7-COOH

Classification of Fatty Acids

1. Based on Saturation
2. Saturated Fatty Acids (SFAs)

• No double bonds between carbon atoms.
• Solid at room temperature (e.g., butter, animal fat).
• Straight-chain structure allows tight packing → higher melting points.

Examples:

• Palmitic acid (C16:0) → Found in palm oil.
• Stearic acid (C18:0) → Found in cocoa butter.

1. Unsaturated Fatty Acids (UFAs)

• One or more double bonds present.
• Liquid at room temperature (e.g., vegetable oils).
• Bent structure due to cis double bonds → prevents tight packing.

Types:

• Monounsaturated Fatty Acids (MUFAs) → One double bond. Example: Oleic acid (C18:1) (olive oil).
• Polyunsaturated Fatty Acids (PUFAs) → Two or more double bonds. Example: Linoleic acid (C18:2, ω-6), Linolenic acid (C18:3, ω-3).

Cis vs. Trans Isomers:

• Cis (natural form) → Bent structure, found in plants.
• Trans (artificial form) → Linear structure, found in hydrogenated oils.

2. Based on Chain Length

• Based on Essentiality

i) Essential Fatty Acids (EFAs) Cannot be synthesized by the human body. Must be obtained from diet. Examples: Linoleic acid (ω-6) → Found in sunflower oil. α-Linolenic acid (ω-3) → Found in flaxseed oil.

ii) Non-Essential Fatty Acids: Can be synthesized in the body. Examples: Palmitic acid (C16:0), Oleic acid (C18:1)

Properties of Fatty Acids

1. Physical Properties

• Solubility → Insoluble in water, soluble in non-polar solvents.
• Melting Point → Depends on chain length and degree of saturation.
  • Saturated FA → Higher melting points (solid at room temp).
  • Unsaturated FA → Lower melting points (liquid at room temp).

2. Chemical Properties

• Esterification → Reacts with alcohols to form esters (e.g., triglycerides).
• Hydrolysis → Splits into glycerol and free fatty acids in the presence of water and enzymes.
• Hydrogenation → Converts unsaturated FA to saturated FA (used in margarine production).
• Oxidation (Rancidity) → Leads to spoilage of fats and oils.

Summary Table