High-Molecular Compounds and Chemistry of Life
High-Molecular Compounds and the Chemistry of Life covers polymers and their monomers, then the structure and reactions of carbohydrates, proteins, fats and nucleic acids.
Core rules
- Addition polymerisation (polyethylene, PVC, polystyrene, PTFE) opens C=C bonds; no small molecule is lost and the repeat unit has the same formula as the monomer.
- Condensation polymerisation (nylon-6,6, PET, phenol–formaldehyde) releases water or HCl; the repeat unit is smaller than the monomers combined.
- Degree of polymerisation = M_polymer / M_repeat unit.
- Starch is a branched polymer of α-glucose, digested by amylase; cellulose is linear β-1,4-glucose, indigestible by humans.
- Reducing sugars (glucose, maltose, lactose) reduce Tollens' and Fehling's reagents; sucrose does not.
- Amino acids are amphoteric zwitterions; the peptide bond forms between –COOH and –NH₂ with loss of water. Denaturation disrupts hydrogen bonds, not peptide bonds.
- Fats are triglycerides; alkaline hydrolysis (saponification) gives glycerol and soap.
Worked example
A polyethylene sample has M = 2.8 × 10⁵ g/mol. The repeat unit –CH₂–CH₂– has M = 28 g/mol, so the degree of polymerisation is 2.8 × 10⁵ / 28 = 1.0 × 10⁴. Note that the repeat unit is C₂H₄, not the C₂H₆ you would obtain by adding hydrogen to the monomer.
Traps
- Using the monomer molar mass for a condensation polymer without subtracting the small molecule released.
- Claiming cellulose is a direct glucose source for humans.
- Describing denaturation as hydrolysis of peptide bonds.