Electrophillic addition

• What is heterolytic fission?

  Breaking a bond with both electrons going to one atom
• What do alkenes contain at least one of?

  A double bond
• What does a double bond in alkenes consist of?

  A sigma bond and a pi bond
• How many electrons does a double bond in alkenes consist of?

  Four electrons
• Why do alkenes react through electrophilic addition?

  Due to the region of high electron density
• What are the three hydrogen halide molecules mentioned?

  Hydrogen chloride, hydrogen bromide, hydrogen iodide
• What does the permanent dipole in hydrogen halides indicate?

  Halogen atoms are more electronegative than hydrogen
• What charge does the hydrogen atom have in hydrogen halides?

  A small positive charge
• What charge does the halogen atom have in hydrogen halides?

  A small negative charge
• What happens when hydrogen bromide approaches an alkene?

  The positive hydrogen is attracted to the double bond
• What is the role of the positive hydrogen atom in hydrogen bromide?

  It acts as an electrophile
• What happens to the pair of electrons in the pi bond of the alkene?

  They move towards the hydrogen atom
• What do curly arrows represent in reaction mechanisms?

  The movement of electron pairs
• What forms when a covalent bond is created towards the hydrogen atom?

  A covalent bond forms with the hydrogen atom
• What is the limitation of a hydrogen atom in bonding?

  It can only have one covalent bond
• What happens to the electrons in the covalent bond between hydrogen and bromine?

  They move to the bromine atom
• What is formed after the reaction between the alkene and hydrogen halide?

  A positively charged carbocation intermediate
• Why is the carbon atom in the carbocation positively charged?

  It lost its share of the electron pair
• What is the charge of the bromide ion formed in the reaction?

  Negatively charged
• What happens to the electron pair on the bromide ion?

  It is attracted to the positive carbon atom
• What product is formed when the bromide ion bonds with the carbocation?

  Bromoethane
• What type of reaction is the addition of hydrogen bromide to ethene?

  Electrophilic addition
• What is unique about the alkene ethene in this reaction?

  It is a symmetrical molecule
• What happens when the reaction is carried out with an asymmetric alkene?

  Two possible products can be formed
• How to make a major product

  1. In the second stage, draw the carbocation that’s most stable
  2. This means add the plus sign to the carbon atom that has the most carbons attatched
  3. Add the H to the other one
  4. Carry on as normal
• how to make the minor product

  1. In the second stage, draw the carbocation that’s least stable
  2. This means add the plus sign to the carbon atom that has the least carbons attatched
  3. Add the H to the other one
  4. Carry on as normal
• Why is a product formed a major product

  The product is formed via a more stable carbocation due to electron releasing character
• Why’s there a attraction between br2 and a carbon double bond

  Br2 gets polarised by the region of high electron density and the electronegative atom to the electronegative +
• What does this mechanism do

  Turns alkene to haloalkane or (in hydration alkene to alcohol )
• What else does this mechanism do

  Turns Alkene to alcohol using conc h2so4
• What must be all specified when explaining why a chemical is a major product?

  Always compare the classes of the carbocations do not say ‘more stable’