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 x 100 theoretical yield

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 + H 2 ) 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 hydrolysis with NaOH produces soaps fatty acids are straight-chain carboxylic acids, C 4 to C 24 ; 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 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