Organic 3: Halogenoalkanes

Because halogens are more electronegative than carbon So the electrons are drawn towards the halogen Making the carbon delta positive (electron deficient) And the halogen delta negative

Halogenoalkanes are insoluble in water because the polar C-X bonds are not polar enough to interact with polar water molecules

Boiling points increase with increased carbon chain length Also increase going down the halogen group Both are because of increased van der Waal forces

1) Increased molecular mass due to halogen - more van der Waals, higher boiling point 2) Polarity increases strength of IMFs (i.e. dipole-dipole bonding) so more energy needed to overcome IMFs

Bond polarity Bond enthalpy (more important)

More polar bonds are more reactive More electronegative halogens attract more electrons in the C-X bond Making the carbon atom more delta positive (electron-deficient) So more attractive to nucleophiles (electron pair donors)

A donor of a lone pair of electrons

Bonds get weaker down the group Because atomic radius increases So force of attraction between the valence electron involved in the C-X bond and nucleus is weaker So the C-X bond is weaker If the bond is weaker, it is easier to break, So a lower bond enthalpy makes a halogenoalkane more reactive

1) Amine 2) Alcohol 3) Nitrile

Nucleophilic substitution Reagents = Ethanolic aqueous NaOH or KOH Conditions = Warm :OH- acts as nucleophile Na/K from NaOH/KOH react with halide nucleophile produced

Mechanism = Nucleophilic substitution Reagents = Ethanolic aqueous KCN Conditions = Warm :CN- acts as nucleophile K from KCN reacts with halide nucleophile produced

Nucleophliic substitution Reagents = Excess ethanolic concentrated ammonia Conditions = Under pressure :NH3- acts as nucleophile NH4+ reacts with halide nucleophile to produce ammonium halide

1) X is more electronegative than carbon, so attracts the electrons in the C-X bond, making the carbon partially positive so attractive to nucleophiles 2) Nucleophiles donate their lone pair to the delta positive carbon atom 3) The C-X bond breaks, and a bond forms between the nucleophile and carbon atom 4) The halogen is removed as the leaving group with its pair of electrons, forming a halide ion

1) A proton must be lost from the NH3 group to form the neutral amine NH2 2) The lone pair from a second ammonia molecule is attracted to the delta positive hydrogen atom, removing the H+ and forming a bond to produce an ammonium ion

Eliminiation Reagent: Hot ethanolic KOH or NaOH Conditions: Heat OH- ion acts as a base Produces water and a halide ion which reacts with K or Na to produce KX or NaX

1) The OH- ion uses its lone pair to form a bond with one of the hydrogen atoms on the carbon next to the C-X bond because these hydrogens are slightly delta positive 2) The electron pair from the C-H bond becomes part of the carbon-carbon double bond 3) The halogen takes the pair of electrons in the C-X bond and leaves as a halide ion

Halogenoalkanes that contain chlorine and fluorine but no hydrogen atoms They decompose in the atmosphere to give chlorine atoms Which decompose ozone, breaking down the ozone layer