Revision notes · Organic chemistry
Synthetic and naturally occurring polymers
Addition polymerisation4.7.3.1
Definition: Addition polymerisation is a reaction where many small unsaturated alkene monomers join together to form a single long-chain polymer.
In addition polymerisation, double bonds open up to join alkene monomers together into long chains.
- •Monomers must contain a carbon-carbon double bond (C=C).
- •The carbon-carbon double bond opens up to form single carbon-carbon bonds connecting the repeating units.
- •The repeating unit contains the exact same atoms as the monomer because no other molecule is formed.
- •Poly(ethene) is formed from ethene monomers, and poly(propene) is formed from propene monomers.
⚠️ Common mistake: Thinking that addition polymerisation produces a small byproduct molecule like water.
🧠 Remember: Addition = Double bond opens, only ONE product is formed.
Condensation polymerisation4.7.3.2
Definition: Condensation polymerisation is a reaction where monomers with two functional groups join together, losing small molecules such as water.
Condensation polymerisation joins monomers together while eliminating a small molecule byproduct.
- •Monomers do not need a carbon-carbon double bond, but each monomer must have two functional groups.
- •The simplest condensation polymers are formed from two different monomers, each having two of the same functional group.
- •An example is polyester, formed from a diol (two alcohol groups) and a dicarboxylic acid (two carboxylic acid groups).
- •For every linkage formed in the polymer chain, a small molecule of water (H₂O) is lost.
⚠️ Common mistake: Confusing addition and condensation polymerisation: condensation always produces a small molecule byproduct alongside the polymer.
🧠 Remember: Condensation = 2 functional groups per monomer plus a water byproduct.
Amino acids4.7.3.3
Definition: An amino acid is an organic molecule containing two different functional groups: an amino group (-NH₂) and a carboxylic acid group (-COOH).
Amino acids react via condensation polymerisation to form polypeptides and proteins.
- •Every amino acid contains a basic amino group (-NH₂) and an acidic carboxylic acid group (-COOH).
- •Amino acids react by condensation polymerisation to produce long chains called polypeptides.
- •During polymerisation, the amino group and carboxylic acid group react, producing a molecule of water.
- •Different amino acids can be combined in the same chain to produce a vast range of different proteins.
⚠️ Common mistake: Forgetting that amino acids contain two different functional groups in the exact same molecule.
🧠 Remember: Amino group + Acid group = Polypeptide + Water.
DNA (deoxyribonucleic acid) and other naturally occurring polymers4.7.3.4
Definition: DNA (deoxyribonucleic acid) is a large, naturally occurring polymer made of nucleotide monomers that encodes genetic instructions.
DNA and many other essential biological molecules are polymers produced naturally by living organisms.
- •DNA is made from four different monomers called nucleotides.
- •A DNA molecule consists of two polymer chains twisted around each other to form a double helix.
- •Other naturally occurring polymers essential for life include proteins, starch, and cellulose.
- •Wool is a natural fibre made almost entirely of the protein keratin — if a question asks for the natural polymer in wool, the answer is protein.
- •Both starch and cellulose are natural polymers made from glucose (sugar) monomers.
⚠️ Common mistake: Stating that DNA is made from amino acids instead of nucleotides.
🧠 Remember: DNA = Nucleotide monomers in a Double helix.
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