2B3 Amines, amino-acids and polymers

• Physical properties

  • N atom is very electronegative so the N-H bond is polarized and leads to moderate levels of intermolecular bonding between amines
  • boiling and melting points are higher than alkanes of similar Mr values
• Base properties

  • lone pair of electrons on the N
  • used to make a coordinate bond with a H+
  • nucleophiles
  • if dissolved in water they produce alkaline solutions
  • very soluble in water except phenylamine
• Relative strength of bases

  • aliphatic amines have the strongest base properties, then ammonia, then phenylamine
  • R groups are electron-rich as a result of being fully saturated is has a positive effect towards the nitrogen
  • makes the lone pair on the N more available for the H+ and the coordinate bond forms more easily
• Aliphatic amines are stronger bases than ammonia
• Aromatic amine base properties

  • weak bases
  • benezene ring has a negative effect on the lone pair on the N
  • overlaps with the delocalised pi ring
  • makes the lone pair les available for reaction making
• Aromatic amines are less strong bases than ammonia
• Preparation of amines

  • aliphatic amines made from haloalkanes with conc. ammonia in a nucleophilic substitution reaction
  • secondary and tertiary amines are made if the haloalkane is in excess it reacts with the amine itself
  • s quaternary ammonium salt can be formed which can be cationic surfactants as they have 3 long alkyl chains
• Amine reactions with acyl chlorides and acid anhydrides

  • nucleophilic addition- elimination reactions
• Preparations of amines

  • nucleophilic substitution: haloalkanes, excess ammonia, requires heat and reflux in a sealed tube
  • reduction of nitriles: hydrogen gas, nickel catalyst, high temperature (only produces one product)
  • reduction of nitrobenzene: form phenyl amine, uses tin, hydrochloric acid or hydrogen and nickel catalyst
• Stereoisomerism

  • isomers have the same molecular and structural formula
  • geometrical isomerism: occurs in alkenes, E-Z isomers and cis-trans isomers
  • optical isomers
• Optical isomers

  • group of isomers that have one spatial difference which leads to two possible stero-isomers
  • only difference is the way they affect a particular type of light
  • molecule must contain a chiral centre
  • enantiomers
  • polarised light affected
  • if there is an equimolae mixture of the two enantiomers the effects cancel out and the mixture is optically inactive called a racemic mixture
• Amino-acids

  • contain 2 functional groups; amino and carboxylic acid
  • have basic and acidic groups
  • R groups can form enantiomers
  • L- amino acids only form of optical isomers found in living systems
• Acid and base properties of amino acids

  • extensive H bonding
  • pure amino acids are ionic and the acid group loses a H+ and donates it the amino acid to form a zwitterion
  • ions then become strong ionic lattices, extremely soluble in water
  • in acidic solutions the NH2 group accepts another H+ to form a cation
  • in alkaline solutions the COOH group loses a H+ to form an anion
• Proteins

  • formed in condensation reaction of amino acids
  • linked by peptide bonds
  • no chemical difference between a polypeptide and a protein
  • protein is directional
• Hydrolysis of proteins

  • break down of proteins as the peptide bond is broken
  • enzymes in living systems
  • in a lab done by heating the protein with strong acid or sodium hydroxide
  • acid group forms a carboxylate ion
• H-bonding in proteins

  • backbone is regular and forms a spiral
  • spiral can fold in random ways depending on the R group attached at the chains
  • spirals can lie alongside other spiral chains by forming H bonds between chains which allows the protein to form fibres which are found in certain tissues
• Condensation polymerisation

  • polymers formed by condensation reactions
  • the be able to manufacture a chain the molecules involved have to be bifunctional i.e. they have to have a suitable group of both ends of the molecule
• Polyesters

  • involves reactions between a dicarboxylic acid and a diol
  • an addition-elimination reaction occurs between the acid and the alcohol groups forming an ester
  • polyesters are used in clothing fibres
• Polyamides

  • condensation polymers formed from a carboxylic acid group and an amine group which produces a substituted amine group
  • reaction involved a dicarboxylic acid and a diamine
  • condensation reaction occurs between the acid and amine groups eliminating water
• Hydrolysis of polyesters and polyamides

  • hydrolysed by heating dilute HCl or dilute NaOH
  • both polymers biodegradable