OZ 3

• Halo alkanes

  Alkanes with one or more halogen attached to them
• Naming examples

  • Trifluoroethane
  • 2-chlorobutane
  • 1-bromo-1,1-dichloroethane
• The slides used in the video are available for purchase by clicking on the link in the description box
• The video is presented by Chris Harris from a website called Luriecheaters.com
• Halo alkanes have polar bonds and are attacked by nucleophiles due to the electronegativity of halogens pulling electrons towards themselves
• The video provides an overview of the halo alkanes part of the ozone story topic in Salters
• The video is on halo alkanes for OCR be Salters
• The slides are dedicated to the Salters specification and map the specification points listed in the syllabus from Salters
• Naming halo alkanes

  Find the longest carbon chain, name the halogens as prefixes in alphabetical order with numbers to state their positions on the carbon chain
• Boiling points of halo alkanes increase as you go down the group due to the increase in the number of electrons in the halogen, leading to stronger intermolecular forces
• Nucleophile

  A substance that is an electron pair donor
• Nucleophilic substitution reaction

  Occurs when alkanes react with hydroxide ions under warm aqueous sodium hydroxide conditions
• Reaction with water

  Occurs via nucleophilic substitution under heat and base conditions
• Nucleophiles

  • Ammonia, water, hydroxide ions
• Compounds with polar bonds are attacked by nucleophiles
• Nucleophilic substitution mechanism

  1. Nucleophile attacks the Delta positive carbon, replacing the halogen

  2. Formation of a bond between the nucleophile and the carbon

  3. Heterolytic break of the bond with electrons moving to the halogen

  4. Formation of an alcohol and a halide
• Formation of an intermediate in the reaction with water

  1. Water attacks the Delta positive carbon, replacing the halogen

  2. Formation of an intermediate with a positive charge on oxygen

  3. Breakage of the O-H bond to form alcohol and H+ ion

  4. Interaction of H+ ion with chloride ion to balance charges
• Formation of alcohol from C

  Formation of alcohol from C, production of H+ ion, interaction with chloride ion, ensuring charges are balanced
• Evidence for reactivity based on reacting haloalkanes with silver nitrate
• Haloalkanes become more reactive as we go down the group
• Reactivity of carbon-halogen bonds

  • CI bond
  • CB bond
  • CI bond
• Reactions with CI bond are the most reactive compared to reactions with CF bond
• Nucleophilic substitution with ammonia

  Reaction with ammonia, conditions needed: heat, ethanolic ammonia, excess ammonia, attack on Delta positive carbon, formation of intermediate, addition of NH3 onto the molecule, formation of ammonium ion
• Bond strength or bond enthalpy determines the reactivity of haloalkanes, not bond polarity
• Formation of silver iodide, silver bromide, and silver chloride based on bond strength
• The next strongest bond after the strongest one is bronze chloride
• Bond fishing involves two types: homolytic and heterolytic
• Propagation in free radical chain reactions involves radicals reacting with non-radicals to create new radicals, continuing the chain reaction
• Homolytic bond fishing

  The bond breaks and the pair of electrons in the bond are shared equally to form two radicals
• The set of rules for free radical chain reactions can be used to make haloalkanes like bromomethane
• Heterolytic bond fishing

  The bond breaks but the electrons are distributed equally to form two different ions
• Termination in free radical chain reactions occurs when two radicals collide to form a non-radical molecule, ending the reaction
• Bronze chloride forms the slowest and has the strongest bond density between the car and the chlorine
• Initiation in free radical chain reactions involves breaking bonds homolytically using UV light to produce highly reactive radicals
• Initiation in making bromomethane involves breaking the Br-Br bond using UV light to produce highly reactive radicals
• Free radical chain reactions

  1. Initiation: Radicals are produced using UV light to break bonds homolytically

  2. Propagation: Radicals react with non-radicals to create new radicals

  3. Termination: Two radicals collide to form a non-radical molecule, ending the reaction
• Radical produced in the second propagation stage is always the radical used in the first stage as a reactant
• CFCs, chlorofluorocarbons, break down ozone in the stratosphere
• The frequency of UV radiation determines the ability to break CFC bonds
• CFCs are broken down by UV radiation in the stratosphere, forming radicals like fluorine and alkane radicals