haloalkanes

• Describe and explain the rate of hydrolysis down group 7

  -increase down group 7
• What are haloalkanes?

  compounds containing the elements carbon, hydrogen and at least one halogen
• What are primary haloalkanes?

  the halogen is attached to a carbon atom which is attached to one other carbon atom

  
• What are secondary haloalkanes?

  the halogen is attached to a carbon atom which is attached to 2 other carbon atoms

  
• What are tertiary haloalkanes?

  the halogen is attached to a carbon atom which is attached to 3 other carbon atoms

  
• Why do tertiary haloalkanes have a faster rate of reaction than secondary and primary haloalkanes?

  tertiary carbocations are more stable than secondary and primary carbocations
• Are haloalkanes polar or non-polar molecules?

  polar as the halogen atoms are more electronegative than carbon atoms
• What is a nucleophile?

  an atom (or group of atoms) that is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond
• Illustrate and explain the nucleophilic substitution mechanism of chloroethane and a hydroxide ion

  1) OH- nucleophile approaches carbon on opposite side of halogen to reduce repulsion

  2) Lone pair of electrons on OH- ions is attracted and donated to the partially positive carbon atom

  3) New covalent bond formed between oxygen of OH- ion and carbon atom

  4) Carbon-halogen bond breaks by heterolytic fission

  5) Alcohol and halide ion formed

  
• What are 3 examples of a nucleophile?

  OH-, H2O, NH3
• What is nucleophilic substitution?

  a chemical reaction in which an atom or group of atoms is exchanged for a nucleophile
• How can haloalkanes be converted to alcohols?

  -aqueous sodium hydroxide and heating under reflux

  -nucleophilic substitution mechanism
• Describe and explain the rate of hydrolysis of haloalkanes

  -increases down group 7

  -bond enthalpies decrease, meaning that its easier to break the C-I bond than the C-Cl bond
• How can the rate of hydrolysis of primary haloalkanes be measured?

  -react haloalkanes with water (from aqueous silver nitrate)

  -silver halide precipitate formed= measure the rate of formation
• Why is ethanol needed to measure the rate of hydrolysis of haloalkanes?

  to allow water and haloalkane to mix
• What is an organohalogen?

  molecules that contain at least one halogen atom joined to a carbon atom
• What are the uses of organohalogens?

  -pesticides

  -solvents

  -flame retardants

  -dry cleaning
• Why are ozone molecules necessary for Earth's survival?

  O3 molecules absorb UV-B radiation in the stratosphere, which can cause skin cancer and crop damage
• What were CFCs used for?

  Refrigeration, foam cushions, propellants in aerosol spray, nontoxic solvents for oil and grease
• When do CFCs break down?

  -they are very stable molecules

  -at stratosphere, they break down
• How is ozone formed?

  -high energy UV breaks down oxygen molecules into oxygen radicals

  -steady state if formed= rate of formation of ozone is the same as the rate at which it is broken down

  
• How is ozone broken down?

  -UV radiation provides energy to break a carbon-halogen bond by homolytic fission to form radicals

  -C-Cl bond breaks as it has the lowest bond enthalpy

  -chlorine radicals act as catalysts as it is regenerated and used again and again

  
• How are nitrogen monoxide radicals formed?

  -lightning strikes

  -aircraft travel in stratosphere