Alkenes 🏖️

• what are alkenes?

  unsaturated hydrocarbons with the general formula CnH2n

  they can be branched, polyunsaturated (more than one double bond) and cyclic
• what is the type of bonding that makes up the double bond

  a double bond is made up of a pi and sigma bond

  a pi bond is the sideways overlap of 2 pi bonds

  each carbon atom contributes one electron to the electron pair in the P orbital

  The pi bonds locks the carbon atoms in position and prevents rotation
• how does a c=c look?

  .

  
• what is the shape around a double bond?

  three regions of electron density around each carbon atom= 120’ and a trigonal planar shape
• What are sterioisomers?

  Molecules with the same structural formula but different arrangements of atoms in space.
• what is one main difference between optical and E/Z isomerism?

  E/z can only occur in alkenes because of their carbon carbon double bond but an optical isomer can occur in pretty much any molecule
• what are the two conditions that myst be satisfied for E/Z isomerism?

  has a c=c double bond and has a different group attached to each carbon atom of the double bond

  
• what is the E isomer and what is the Z isomer?

  • Z=sameZ
  • E= oppositE

  
• what is must be present if a molecule has cis/trans isomerism?

  one of the attached groups to carbon must be hydrogen

  • ciS= Z isomer= Same
  • trans= E iso
• how to determine if an alkene just containing one hydrogen is cis or trans?

  using the cahn-ingold-prolog rules

  • high priority groups in the same side= Z isomer
  • high priority groups in diagonal= E isomer
  • priority is based on atomic number
• what is the reactivity of an alkene relative to an alkane?

  They are more reactive as a pi bond is weaker than a sigma bond and therefore can be broken with less energy
• What happens when an alkene react with hydrogen halide?

  addition reaction

  if alkene is unsymmetrical = two possible products

  • product that has hydrogen from hydrogen halide attached to the carbon atom already attached to the most hydrogen atoms = major product

  
• what is an electrophile?

  electron deficient atom that is attracted to a electron rich centre nand accepts an electron pair

  • electron pair acceptor
• what is the mechanism for the reaction between propene and bromine?

  .

  
• using markownikoff’s rule to determine whether the products from electrophilic addition is major or minor?

  • primary carbocation= positive charge on first carbon= smaller yield= minor product
  • secondary= positive charge is on cation that is attached to 2 other carbons= major product

  
• how can you determine the stability of a carbocation?

  eah alkyl groups donates electrons toward the carbon with the positive charge, the more alkyl groups the more stronger attraction to the positive charge and the stronger the spread of the charge= more stable ion

  • primary carbocation= least and the tertiary carbocation= most stable
• What are problems with disposing of waste polymers?

  • lack reactivity= good for storing food= used a lot and thrown away
  • Most= non-biodegradable