ORGANIC CHEMISTRY 2
ATIKAHBENNY YODI SDESY INDRA WHIDAYATULLAH
MAYSAROH
LIPIDS
INTRODUCTIONLipids are compounds of biological origin that dissolve in nonpolar solvents, such as
chloroform and diethyl ether. The name lipid comes from the Greek word lipos, for fat.
DEFINITIONLipids can best be defined as
biomolecules which are soluble to a great extent in nonpolar solvents.
Lipids can be categorized as hydrolyzable or nonhydrolyzable
• Hydrolyzable lipids can be cleaved into smaller molecules by hydrolysis with water. Most hydrolyzable lipids contain an ester unit. We will examine three subgroups: waxes, triacylglycerols, and phospholipids.
• Nonhydrolyzable lipids cannot be cleaved into smaller units by aqueous hydrolysis. Nonhydrolyzable lipids tend to be more varied in structure. We will examine four different types: fat-soluble vitamins, eicosanoids, terpenes, and steroids.
WAXES
Waxes are the simplest hydrolyzable lipids. Waxes are esters (RCOOR') formed from
a high molecular weight alcohol (R'OH) and a fatty
acid (RCOOH).
The structure of this compound shows how small the ester
group is compared to the long hydrocarbon chains.
Wax is a generic term that encompasses materials that have some specific properties such as:
• Solid at 20C, varying from soft / plastic to brittle / hard
• A melting point > 40C without decomposing
• A relatively low viscosity slightly above the melting point
• Transparency to opaque, but not glass-like
• Buffable under slight pressure
TRIACYLGLYCEROLS
Triacylglycerols, or triglycerides, are triesters that produce glycerol and three molecules of fatty acid
upon hydrolysis. Simple triacylglycerols are composed of
three identical fatty acid side chains, whereas mixed
triacylglycerols have two or three different fatty acids.
The characteristics of fatty acids
• All fatty acid chains are unbranched, but they may be saturated or unsaturated.
• Naturally occurring fatty acids have an even number of carbon atoms.
• Double bonds in naturally occurring fatty acids generally have the Z configuration.
• The melting point of a fatty acid depends on the degree of unsaturation.
• Fats and oils are triacylglycerols; that is, they are triesters of glycerol and these fatty acids. – Fats have higher melting points, making
them solids at room temperature. – Oils have lower melting points, making
them liquids at room temperature.
As the number of double bonds increases, the melting point decreases, as it does for the constituent fatty acids as well.
NOMENCLATURE
• Short-hand notations can be written for the fatty acids which indicate the number of carbons/ number of double bonds/ positions of double bonds from the carboxyl end of the molecule;
for example, linoleic acid would be C18:2∆9, 12. • Another way to describe unsaturated fatty acids
denotes the position of the first double bond from the alkyl end of the molecule; for example, linoleic acid would be ω6.
Hydrolysis of triacylglycerols
Hydrogenation of unsaturated fatty acids
Oxidation of unsaturated fatty acids
Saturated fat acid reaction
Unsaturated fat acid reaction
Saponification
Soap and detergent
Structure of Soaps
• A soap molecule has a nonpolar, alkyl end and a polar, salt end. Because of this dual polarity, it is called amphipathic. This hydrophobic/hydrophilic nature is essential to the function of such molecules.
Mechanism of Soap Action
• The cleaning action of soap involves lowering the surface tension of water by disrupting hydrogen bonds at the surface and the formation of micelles within the volume of water present. Micelles are aggregrations of soap molecules arranged so that the hydrophobic “tails” are oriented towards each other away from the water solvent and the hydrophilic “heads” are pointed into the water.
Detergents
Detergents are amphipathic molecules which have enhanced solubility and biodegradability properties compared to soaps. Instead of having a sodium salt in the polar portion of the molecule, other ionic and polar groups are used giving rise to what are called "cationic", "anionic" and "nonionic" detergents.
PHOSPOLIPIDS
Phospholipids are hydrolyzable lipids that contain a phosphorus atom. There are two common types of phospholipids: phosphoacylglycerols and sphingomyelins.
Phosphoacylglycerols
• When R'' = CH2CH2NH3+, the compound is called a phosphatidylethanolamine or cephalin.
• When R'' = CH2CH2N(CH3)3+, the compound is called a phosphatidylcholine, or lecithin.
Sphingomyelins
• Other notable features of a sphingomyelin include:
= • A phosphodiester at C1. = • An amide formed with a fatty acid at C2.
FAT-SOLUBLE VITAMINS
EICOSANOIDS
The word eicosanoid is derived from the Greek word eikosi, meaning 20.
TERPENES
Terpenes are lipids composed of repeating five-carbon units called isoprene units. An iso- prene unit has five carbons: four in a row, with a one-
carbon branch on a middle carbon.
• An isoprene unit may be composed of C– C σ bonds only, or there may be π bonds at any position.
• Isoprene units are always connected by one or more carbon–carbon bonds.
• Each carbon atom is part of one isoprene unit only. • Every isoprene unit has five carbon atoms.
Heteroatoms may be present but their presence is ignored in locating isoprene units.
STEROIDS
Steroids are important “biological regulators” that nearly always show dramatic physiological effects when they are administered to living organisms. Among these important
compounds are male and female sex hormones, adrenocortical hormones, D vitamins, the bile acids, and
certain cardiac poisons. Steroids are derivatives of the following perhydrocyclopentanophenanthrene ring
system:
REACTION
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