Haloalkanes 👷

• What are haloalkanes?

  Compound containing carbon, hydrogen and at least one halogen

  when there is two or more halogens they are listen in alphabetic order

  aliphatic haloalkanes can be primary, secondary and tertiary
• what type of bonding does a haloalkane have?

  • carbon and halogen= very different electronegativity
  • halogen= more electronegative= electron pair is closer
  • polar= temporary charges- carbon gain slightly positive charge= attracts lone pair of electron because it is slightly deficient
  • nucleophile donates electron pair to carbon to form new covalent bond= nucleophillic substitution
• what are nucleophiles?

  species that donate a lone pair of electrons and is attracted to an electron deficient carbon atom

  
• what is hydrolysis and what does it occur with?

  is when a primary haloalkane nucleophilic substitution where the halogen atom is replaced by the -OH group

  • OH approaches carbon atom that is on the opposite side of the halogen atom= minimises repulsion between nucleophile and the delta neg halogen
  • Lone pair of hydroxide is attracted to the carbon atom= donated
  • carbon and halogen bond breaks by heterolytic fission and a new bond forms between the oxygen atom and carbon
  • new product= alcohol+ halide ion

  
• What are the conditions needed to convert haloalkanes into alcohols?

  Aqueous sodium hydroxide and heated under reflux to increase rate of reaction
• What does the rate of hydrolysis depend on?

  The strength of the carbon-halogen bond

  • C-F = strongest bond
  • C-I = weakest
  • iodoalkanes, bromoalkanes, chloroalkanes in terms of fastest to slowest reaction
  • fluoroalkane requires too much energy to break bonds= unreactive

  also depends on the type -of haloalkane

  • primary is slowest and tertiary is fastest
• What is the ozone layer and what is its job?

  • Ozone layer= found outer edge of stratosphere= made up of a tiny fraction of ozone= absorb most of the biologically damaging UV radiation from the sun
  • if ozone= depleted= not enough UV is absorbed= genetic damage and skin cancer risk= increase
  • step 1: very high energy breaks down oxygen molecules into oxygen radicals
  • a steady state is formed with the new O2 being created and the oxygen radicals that were previously created= human activity and CFCs can distrust this equilibrium

  
• What are CFCs and HCFCs used as and why?

  • used as refrigerants in AC units and as aerosol propellants
  • CFCs are very stable because of the strength of the carbon halogen bond
• what is the impact of CFCs on the environment and why?

  CFC’s remain stable until they reach the stratosphere- begin to break down into chlorine radicals- catalyse break down of ozone layer

  • CFC has strong carbon-halogen bonds= stable in troposhere
  • reach stratosphere= UV radiation= provide enough energy to break bonds by homiletic fission --> called photodissociation
  • chlorine radicals= now formed= very reactive intermediate= can react with ozone molecule
  • the chlorine radical formed in propagation 2 can go attach ozone in step one= cycle

  
• How many Ozone molecules can a single CFC molecule breakdown?

  100 000
• Are CFCs the only reason for ozone depletion?

  Other radicals can catalyse the breakdown of ozone eg nitrogen oxide radicals that are formed when lightning strikes or aircraft travel in the stratosphere

  • the overall equation is the same as when it was chlorine radicals