Halogenoalkanes

• What are the steps of free radical substitution?

  Initiation, propagation, termination.
• How can you classify halogenoalkanes?

  Primary, secondary and tertiary
• What reactions can halogenoalkanes undergo?

  Nucleophilic substitution and elimination
• What is a nucleophile?

  An electron pair donor
• What is the mechanism for this reaction?

  The nucleophile attack the positive carbon atom

  The carbon is slightly positive due to the difference in electronegativity between the carbon and halogen.

  
• Which halogenoalkanes is the fastest to substitute and which halogenoalkanes is the slowest?

  fastest: iodoalkanes

  slowest: fluoroalkanes
• What is a primary halogenoalkane?

  When the halogen is attached to a carbon atom that has one carbon attached to it
• What is a secondary halogenoalkane?

  When the halogen is attached to a carbon with 2 alkyl groups attached to it
• What is a tertiary halogenoalkane?

  A halogenoalkane with the halogen atom attached to a carbon atom that is bonded to three other carbon atoms.
• What happens to the polarity of the C-X Bon down the group?

  Decreases as the group 7 atoms will become less electronegative
• What forces act upon halogenoalkanes?

  permanent dipole-dipole and van der Waals
• What are some of the physical properties of halogenoalkanes?

  They aren’t soluble in water

  As the chain length increases, the boiling point also increases as it has stronger vdW to break

  The C-X bond enthalpy decreases going down the group as outer electrons are closer to the nucleus so. Greater force of attraction

  The reactivity of halogenoalkanes down group 7 increases as bond enthalpy decreases so more reactive as the bond can be broken more easily
• Where does a curly arrow begin?

  At the start of a lone pair of electrons or from the centre of a bond
• What is hydrolysis?

  The splitting of a molecule by the addition of water
• What nucleophiles react with halogenoalkanes?

  Hydroxide ion :OH-, ammonia :NH3, cyanide ion :CN-
• What’s a substitution reaction?

  A reaction in which a species takes the place of another atom or group in a molecule
• What does a curly arrow show?

  The movement of electrons
• What dos the nucleophile substitution with aqueous hydroxide ions form?

  Alcohol
• What s the reagent when halogenoalkanes form an alcohol?

  AQUEOUS sodium/ potassium hydroxide. Ethanol is used as a solvent to ensure the reactants mix together
• What are the conditions for the nucleophilic substitution of :OH?

  Heat under reflux
• What does the reaction of halogenoalkanes and :CN produce?

  Nitriles
• What are the reagents in the nucleophile substitution of :CN?

  aqueous alcoholic solution of potassium cyanide
• What are the conditions for the reaction between halogenoalkanes and :CN?

  Heat under reflux
• What is the product when you react halogenoalkanes and ammonia?

  Amines
• What is the reagent in the nucleophilic substitution with ammonia?

  Excess concentrated solution of ammonia in ethanol
• What are the conditions of the nucleophilic substitution of halogenoalkanes with ammonia?

  Carried out under pressure
• What is an elimination reaction?

  A reaction in which an atom or a group of atoms ar removed from a reactant
• What reaction occurs when halogenoalkanes react with alcoholic hydroxide ions?

  Elimination
• What role does OH- act in elimination reactions?

  Base
• What are the reagents in the elimination reaction of halogenoalkanes?

  ethanol is sodium/ potassium hydroxide.
• What are the conditions for the elimination reaction of halogenoalkanes?

  heat under reflux
• What is the mechanism of the elimination reaction?

  The mechanism

  
• What is the test for alkenes?

  Bromine water test.
• What is the positive test for the bromine water?

  If there’s an alkene, the bromine water will turn colourless
• What factors affect substitution or elimination?

  The reaction conditions (aqueous/ ethanolic solutions)

  The type of halogenoalkane (primary, secondary or tertiary)
• What is the ozone layer?

  O3, a gas present in the stratosphere and ozone absorbs UV light in the atmoshere but is referormed in a reversible reaction
• What is the reaction for the depletion of ozone?

  $2O_ 3$<=>3$O_2$
• Why is ozone important?

  Ozone absorbs UV light in the stratosphere and stops much of it reaching Earth. Depletion (decrease) of the ozone layer allows more UV light to reach the surface of the Earth
• What happens when there’s increased amounts of UV light?

  increased risk of sunburn

  accelerated ageing of skin

  skin cancer

  increased risk of cataracts
• What are the properties of CFC’s?

  chemically inert

  low boiling point

  non-toxic

  non-flammable

  insoluble in water