Polymer Revolution

Polymer Revolution

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  • Created by: R_Hall
  • Created on: 04-05-13 17:18

3.4 E/Z Isomerism

  • E/Z isomerism is a type of steroisomerism. Steroisomers have identical molecular formulae and atoms in the same order, but arrangement of atoms in space is different
  • E/Z isomerism occurs as there is a lack of rotation around the C=C double bond, and occurs in molecules where there are two different groups on each C
  • E (trans)- groups on opposite sides of each carbon
  • Z (trans)- groups on same side of each carbon
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5.4 Bonds Between Molecules:Hydrogen Bonding

  • Hydrogen bonding is the strongest type of intermolecular bond. For hydrogen bonding to occur-
  • 1. Large dipole between H atom and a highly electronegative atom (O,F or N)
  • 2. Small H atom, can get close to O, F or N atoms in nearby molecules
  • 3. Lone pair of electrons on O, F or N atom
  • Hydrogen bonding has an affect on the properties of molecules-
  • Boiling point- More hydrogen bonds= higher boiling point. More energy needed to break the intermolecular bonds and separate the molecules
  • Viscosity- More h bonds= higher viscosity. For a liquid to flow, molecules need to move past eachother by breaking bonds. Hard to overcome strong h bonds- lots of energy
  • Solubility- More h bonds= more soluble.H bonds form between molecule and water, helping dissolving process
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5.6 The Structure and Properties of Polymers

  • A polymer is a long molecule made up of many monomers
  • Most polymers formed in reactions called addition polymerisation (single monomers added together). More than one polymer used- copolymerisation
  • Elastomers- soft and springy, go back to original shape eg. rubber
  • Plastics- not springy, deform plastically eg. poly(ethene)
  • Fibres- strong, do not deform easily eg. nylon
  • Characteristics which effect properties-
  • 1. Chain length- longer= stronger
  • 2. Side groups- polar side groups= stronger bonding
  • 3. Branching- straight chains= pack closely= stronger bonding
  • 4. Steroregularity- chains pack closely= stronger bonding
  • 5. Chain flexibility- chains to make more rigid= stronger 
  • 6. Cross linking- linked with covalent bonds= harder and difficult to melt
  • Thermoplastics- have no cross-links between chains, weak forces between chains are easy to break with heating- easily moulded
  • Thermosets- extensive covalent cross-linking, cannot be broken easily when heating, keeps shape
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6.4 Infrared Spectroscopy

  • In infrared spectroscopy, substances are exposed to radiation in the frequency range 10^14 - 10^13 Hz, and wavelength 2.5-15µm. This makes the vibrational energy change within the molecule, causing bonds to absorbs IR of specific frequency 
  • Different bonds absorb infrared radiation of different frequencies, so infrared spectrums can be used to determine a compound
  • Wavenumber is recorded on the infrared spectrum. It is the reciprocal of 1/ wavelength
  • Below 1500 cm-1, the spectrum is very complex and becomes difficult to assign absorptions to particular bonds- fingerprint region
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12.2 Alkenes

  • Alkenes are unsaturated compounds- have a C=C bond. There are cycloalkenes, and when there is more than one C=C, there are dienes
  • Electrophiles are positive ions or molecules with a partial +ve charge that are attracted to -ve regions and react to accept a lone pair of electrons to form a covalent bond
  • Reaction with bromine- bromine becomes decolourised when reacted with an unsaturated compound
  • The bromine molecule becomes polarised as it approaches the alkene. Electrons are pushed towards end of molecule furthest from alkene, making it -ve. +ve bromine is an electrophile, reacts with alkene double bond to form a carbocation
  • The carbocation reacts rapidly with the remaining bromine molecule, forming a bromoalkane. This in an electronphilic addition (two or more large molecules react to forma one molecule) reaction
  • Hydrogen bromide-> bromoalkane
  • Water in presence of catalyst (Phosphoric acid, water as steam, heat and pressure) -> alcohol. Hydration reaction
  • Hydrogen in presence of catalyst (Nickel with heat and pressure, platinum at room temp wth pressure) -> alkane. Hydrogenation
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13.2 Alcohols and Ethers- Reactions of Alcohols

  • Primary alcohols- OH attached to a C atom only attached to H. At end of chain
  • Secondary alcohols- OH attached to a C attached to two other C, and 1 H. In middle of chain
  • Tertiary alcohols- OH attached to C atom which carries to H atoms
  • The -OH group is oxidised by acidified potassium dichromate (K2Cr2O7). It turns from orange to green, and produces a carbonyl group (aldehyde or ketone)
  • Primary alcohols are oxidised to aldehydes, then further oxidised to carboxylic acids
  • Secondary alcohols are oxidised to ketones
  • Tertiary alcohols are not oxidised, as they do not have a H on the C atom which the -OH is attached to
  • Many alcohols can react to lose a molecule of water to form an alkene. Reaction happens under high temperatures and with alumina (Al2O3) acting as a catalyst. This is dehydration, and an elimination reaction (a small molecule is removed from a larger one)
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