3.3.3 Halogenoalkanes Flashcards
Are halogenoalkanes soluable in water?
- No.
- C-H bonds are non-polar, not compensated enough by C-X bond.
Do halogenoalkanes have a polar bond (which part of bond has higher electronegativity)?
- Yes, halogen higher electronegativity than C.
- Halogen δ-.
- Carbon δ+.
What 2 factors affect their boiling points?
- Longer chain.
- Halogen further down grp 7.
Which intermolecular forces do they have?
- Permanent dipole-dipole (due to C-X bond polarity).
- VdW forces of attraction.
Mass of halogenoalkane compared to mass of alkane w/ same chain length?
- Greater, mass halogen > mass H.
Most important factor in reactivity?
- C-X bond enthalpy.
What is the order of reactivity in halogenoalkanes?
- C-X bond enthalpy decreases down group ∴ reactivity increases down the group.
What is a nucleophile?
- Negatively charged ion w/ lone pair of e- which can be donated to an e- deficient atom.
Give 3 examples of nucleophiles.
- :OH-
- :CN-
- :NH3
What is nucleophilic substitution?
- Reaction where nucleophile donates lone pair e- to δ+ C atom.
- δ- atom leaves molecule.
What does CFC stand for?
- Chlorine-fluoro-carbons.
What are CFCs?
- Halogenoalkanes containing C,F + Cl only (no H).
What is the problem w/ CFCs?
- Unreactive under normal conditions.
- Catalyse breakdown of ozone via free radical substitution.
What are CFCs being replaced with?
- HCFCs (H,Cl,F,C).
- HFCs (H,F,C).
What are conditions needed for elimination reaction of halogenoalkanes?
- NaOH or KOH dissolved in ethanol (no H2O present).
- Heated.
What are 3 products formed in elimination reactions of halogenoalkanes?
- Alkene.
- Water.
- Halogen ion.