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Unit 2b The World of Carbon
Carboxylic acids
• contain the carboxyl group, –COOH
• name ends in –oic
• usual rules of naming i.e. longest carbon chain must include –COOH;
number carbon atoms from end closest to –COOH;
branches assigned smallest number possible
e.g.
• Uses: ethanoic acid – pickle food (vinegar), feedstock for paints;
benzoic acid – preservative and antioxidant in food
benzene-1,4-dicarboxylic acid – nylon production
Esters
• contain the ester group, -COO• made by a condensation reaction of an alcohol, –OH, with
an alkanoic acid –COOH giving an ester –COO- + water, H-OH
e.g.
• first part of ester name from alcohol, second part from acid e.g.
pentanoic acid + butan-1-ol makes butyl pentanoate
• the reverse reaction is hydrolysis
• NaOH is often used for hydrolysis, rather than water
Uses of esters
• smelly so useful as flavourings and in perfumes
• solvents, e.g. in paints
• making medicines
Percentage yield
Percentage yield =
actual yield
theoretical yield
x 100
Polymers
-very large molecules made from small monomers
Addition polymers:
• made from unsaturated monomers (usually just the 1)
• alkene monomer
polyalkene product (only!)
• alkenes made by cracking alkanes
• polymers have carbon-to-carbon backbone –C-C-C-C• e.g.
Condensation polymers:
• made from monomers with 2 functional groups
(usually 2 monomers)
• small molecule, usually water, made at same time
• have O, and sometimes N, in backbone
• polyesters, polyamides, methanal-based polymers
Polyesters
• ester group –COO• 1 monomer a diol, the other a diacid
repeating unit in brackets
• linear structures, used for fibres
• additional functional groups in monomers allow
cross-linking between chains; used for resins
Polyamides
• amide group –CONH• usually 1 monomer a diacid, the other a diamine
(protein monomers are amino acids)
this polymer is nylon-6.6
as each monomer has 6
carbon atoms
• hydrogen bonding between chains increases the
strength of the polymer
Methanal based thermosetting polymers
• methanol made from synthesis gas (CO + H2)
and oxidised to methanal
• examples are urea-methanal and Bakelite
• electrical insulators
• thermosetting polymers cannot be remoulded
Newer polymers
Addition polymers
Polyethyne – electrical conductor; used in high performance
loudspeakers
Poly(vinyl carbazole) – photoconductor; used in photocopiers
Poly(ethenol) – water soluble; used in hospital laundry bags
Poly(ethene) with carbonyl groups – photodegradable;
used in packaging material
Condensation polymers
Kevlar – very strong; used in bullet-proof vests
Biopol – biodegradable; high costs have stopped production
Natural Products
Fats and oils
• good energy source
• fats from animals; oils from plants and fish
• esters; hydrolysis produces 1 mole glycerol: 3 moles fatty acids
• fatty acids are straight-chain carboxylic acids, C4 to C24;
can be saturated or unsaturated
• oils more unsaturated, more double bonds than fats. less
densely packed molecules so fewer van der waals interactions
hence lower melting points
• hydrogenation of oils produces fats (vegetable oils
• hydrolysis with NaOH produces soaps
margarine)
Natural Products
Proteins
• natural condensation polymers
• polyamides ie contain many –CONH- groups
• amino acid monomers e.g.
• essential amino acids cannot be made by body, are obtained
through diet
• digestion of proteins produces amino acids
Classifying proteins – 2 types
fibrous: structural materials e.g. in skin, nails, hair
globular proteins: involved in regulation of life processes
e.g. enzymes, hormones. haemoglobin
Enzymes
• specific, only catalyse on reaction
• substrate fits enzyme on ‘lock and key’ principle
• can
be building up reactions, as well as breaking down
• denatured by high temperature, shape irreversibly changed
• optimum pH for activity e.g. pH 2 or pepsin, stomach enzyme