Applications of Functional Groups: Polymers, Soaps, and Lipids

A set of vocabulary flashcards covering the key concepts, classifications, reaction mechanisms, and nomenclature of synthetic polymers, soaps, detergents, and lipids.

Polymer

A large molecule composed of repeating monomer units linked by chemical bonds, typically possessing a molecular weight between $10,000$ and $1,000,000\,\text{g/mol}$.

Monomer

A small molecular subunit capable of chemically bonding to other identical or different molecules to form a polymer chain.

Repeating Unit

The smallest molecular fragment enclosed within brackets that contains all non-repeating structural features of a polymer chain.

Degree of Polymerisation

The average number of repeating units present in a polymer molecule, denoted by the subscript $n$ outside the bracketed repeating unit.

Thermoplastics

Polymers that can be repeatedly melted, poured into moulds, cooled into a shape, and subsequently reheated and reshaped (recyclable).

Thermosetting Plastics

Polymers that can be shaped when first prepared, but upon cooling harden irreversibly through cross-linking and cannot be remelted or remoulded (not recyclable).

Condensation Polymerisation

A polymer formation process occurring between di-functional monomer molecules that releases a small molecule by-product, typically $\text{H}_2\text{O}$, as each linkage forms.

Addition Polymerisation

A reaction where alkene monomers join together by breaking carbon-carbon double bonds to form a polyalkane without the loss of any atoms or creation of small molecule by-products.

Di-functional Monomer

A monomer molecule possessing two reactive functional groups, which may be identical (A-A) or different (A-B), enabling continuous chain growth during condensation polymerisation.

Nylon 66

A synthetic polyamide polymer prepared by the condensation reaction of hexanedioic acid (adipic acid) with 1,6-hexanediamine (hexamethylenediamine).

Kevlar

A lightweight and high-strength polyaromatic amide (polyamide) produced by condensation polymerisation.

Dacron (Mylar)

A strong polyester formed via condensation polymerisation that gains exceptional mechanical strength from aromatic groups incorporated into the polymer backbone.

Free Radical

A chemical species bearing an unpaired electron, making it highly reactive and capable of initiating and propagating addition polymerisation chains.

Addition Polymerisation Mechanism Steps

The three-step radical process consisting of initiation (generating the radical initiator species), propagation (extending the growing chain by successive monomer additions), and termination (halting chain propagation).

Poly(methyl methacrylate) (PMMA)

An addition polymer derived from the monomer methyl 2-methylprop-2-enoate (methyl methacrylate), commonly known as Plexiglass.

Saponification

The base-catalysed hydrolysis of ester functional groups in triglycerides using concentrated alkali (such as $\text{NaOH}$ or $\text{KOH}$) to yield glycerol and fatty acid salts (soaps).

Soap Scum

An insoluble, sticky grey precipitate formed when carboxylate ions of soap combine with divalent or trivalent metal cations ($\text{Ca}^{2+}$, $\text{Mg}^{2+}$, or $\text{Fe}^{3+}$) present in hard water.

Hard Water

Water containing relatively high concentrations of multivalent metal cations, primarily $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, or $\text{Fe}^{3+}$, which interfere with soap functionality.

Synthetic Detergent

A cleaning compound containing a long hydrophobic hydrocarbon tail and a hydrophilic sulfonate head group (such as benzene sulfonate) that remains active without forming precipitates in hard water.

Sodium Dodecyl Sulfate (SDS)

A widely used synthetic detergent and surfactant, also known as sodium lauryl sulfate, featuring a 12-carbon hydrophobic tail and a polar sulfate head group.

Micelle

A spherical colloidal assembly of amphipathic soap or detergent molecules in water, wherein hydrophobic tails sequester inward to trap non-polar grease while hydrophilic heads face outward toward the aqueous solution.

Lipids

A structurally diverse family of biological molecules defined by their shared solubility properties: insoluble in water but readily soluble in non-polar organic solvents.

Saponifiable Lipids

Lipids containing ester functional groups that can be hydrolysed under alkaline conditions, including triglycerides, waxes, and phospholipids.

Non-saponifiable Lipids

Lipids lacking ester functional groups that cannot be cleaved by base hydrolysis, including steroids and prostaglandins.

Fatty Acids

Unbranched, straight-chain carboxylic acids typically $10$ to $22$ carbons in length (usually an even number), occurring in saturated forms or unsaturated forms predominantly featuring cis double bonds.

Essential Fatty Acids

Polyunsaturated fatty acids that humans cannot biosynthesise and must obtain from diet, specifically linoleic acid and linolenic acid.

Linoleic Acid

An essential omega-6 ($18:2\,n-6$) polyunsaturated fatty acid with an 18-carbon chain and two cis double bonds, required to synthesize arachidonic acid and prostaglandins.

Linolenic Acid

An essential omega-3 ($18:3\,n-3$) polyunsaturated fatty acid containing an 18-carbon chain and three cis double bonds.

Triglycerides

Triesters of glycerol (triacylglycerols) formed when three fatty acid molecules condense with the three hydroxyl groups of a single glycerol molecule.

Hardening (Hydrogenation)

The industrial catalytic addition of $\text{H}_2$ across carbon-carbon double bonds in unsaturated vegetable oils to convert them into saturated chains, elevating melting point and firming consistency.

Bile Salts

Steroid-derived amphipathic compounds (such as salts of cholic acid and lithocholic acid) synthesized from cholesterol that act as biological detergents to emulsify dietary fat globules in the gut.

Waxes

High-molecular-weight saponifiable esters composed of a single fatty acid chain bonded to a long-chain alcohol, lacking a glycerol backbone.

Phospholipids

Saponifiable lipids (phosphoglycerides) consisting of a glycerol backbone esterified to two fatty acid tails and a phosphate ester linked to an aminoalcohol.

Lecithin

A common phospholipid, systematically known as phosphatidylcholine, that functions as a natural emulsifying agent in foods such as chocolate and margarine.

Lipid Bilayer

A bimolecular sheet formed by phospholipids in water, held together by hydrophobic interactions such that non-polar hydrocarbon tails face inward away from water while polar heads remain exposed to the aqueous surroundings.

Ergosterol

A fungal membrane sterol that imparts rigidity to the lipid bilayer, serving an analogous biological role to cholesterol in human cells.

Amphotericin B

An antifungal medication obtained from Streptomyces nodosus that selectively binds to fungal ergosterol, compromising membrane integrity and cellular function.

Sphingolipids

A class of complex structural lipids that contain the long-chain aminoalcohol sphingosine in place of glycerol, such as sphingomyelin found in brain and nervous tissue.

Glycolipids

Sphingolipid-based cellular membrane components that incorporate carbohydrate (monosaccharide) residues rather than a phosphate group.

Steroids

Non-saponifiable lipids characterized by a tetracyclic core structure composed of four fused rings (three cyclohexanes and one cyclopentane).

Cholesterol

The most prevalent steroid in the body, which modulates lipid bilayer membrane fluidity and acts as the biosynthetic precursor for bile salts, sex hormones, and vitamin D.

Low-Density Lipoproteins (LDLs)

Lipoprotein complexes responsible for circulating cholesterol, triglycerides, and other lipids from the liver through the bloodstream to tissues throughout the body.

High-Density Lipoproteins (HDLs)

Lipoprotein complexes that collect excess cholesterol and lipids from peripheral cells and tissues and transport them back to the liver.

Prostaglandins

Locally acting, hormone-like non-saponifiable lipids based on a $20$-carbon skeleton containing a cyclopentane ring, biosynthesised from arachidonic acid to regulate inflammation, blood clotting, and pain responses.