Chapter 15: Haloalkanes

compounds containing the elements carbon, (hydrogen) and at least one halogen. i.e. hydrocarbon containing at least one halogen.

halogen is joined to straight/branched carbon chains. Branched carbon chain can be a closed structure - i.e. a ring.

Primary: 1 R group attached to the carbon linked to the halogen Secondary: 2 R groups attached to the carbon linked to the halogen Tertiary: 3 R groups attached to the carbon linked to the halogen

Boiling point - increases with molecular size due to increased intermolecular forces. Straight chain haloalkane isomers have a higher boiling point that branched chain ones. Solubility - haloalkanes are soluble in organic solvents but insoluble in water.

An atom or group of atoms that is attracted to an electron deficient carbon atom, where it donates a pair of electrons to form a new covalent bond. aka electron pair donor

• posses at least 1 lone pair of electrons • electron pair donor • doesn’t need a negative charge

OH-, NH3, CN-, H2O (weak nucleophile)

Reaction in which a nucleophile is attracted to an electron-deficient carbon atom, and replaces an atom or group of atoms on the carbon atom.

• haloalkanes have a C-X bond. Halogen atoms have greater electronegativity than carbon • electron pair in the C-X bond is closer to the halogen than the carbon atom - dipole is induced in the C-X bond • the c-x bond is polar • carbon is thus open to attack by nucleophiles • when a haloalkane reacts with a nucleophile, the nucleophile replaces the halogen in a substitution reaction

Chemical reaction with water that causes the breaking of a bond in a molecule into 2 compounds. H and OH are incorporated into the products.

• dipoles on C-Cl bond • nucleophile (OH- ion) attacks the carbon in such a why that it minimises the repulsion between the nucleophile and the delta negative charge on the halogen • C-Cl bond breaks by heterolytic fission, with the pair of electrons transferring to the chlorine atom to make a negative chloride ion (Cl-) -C-X bond is broken and OH replaces the halogen to form an alcohol • product is an alcohol and a halide ion

• nucleophilic substitution (hydrolysis of haloalkane) • aqueous sodium hydroxide • heated under reflux

R-X + NaOH –> R-OH + NaX

• Depends on the strength of the C-X bond. • The stronger the C-X bond, the less reactive the haloalkane is, the slower the rate of hydrolysis • the weaker the C-X bond, the more reactive the haloalkane is, the faster the rate of hydrolysis

• C-F bond is the strongest, C-I bonds are the weakest • because Iodine has a greater atomic size, increasing the bond length of the C-I bond • the longer the bond length, the weaker the bond strength • less energy is required to break the C-I bond • iodoalkanes hydrolyse faster than fluoroalkanes, which are basically unreactive Order of reactivity (highest to lowest): - iodoalkane - bromoalkane - chloroalkane - fluoroalkane

• Add 1cm3 ethanol and 2 drops of haloalkane to each test tube • Water bath at 60 degrees • Add another test tube of silver nitrate to water bath and let them all reach the same temperature • Add 1cm3 silver nitrate and observe the time take for a precipitate to form in each haloalkane test tube, using a stopwatch.

Water present in aqueous silver nitrate solution AgNO3 (aq)

1-iodobutane will form a precipitate the fastest, then 1-bromobutane, then 1-chlorobutane

Ethanol is used as a solvent since haloalkanes are insoluble in water.

CH3CH2CH2CH2X + H2O –> CH3CH2CH2CH2OH + H+ + X- Ag+ (aq) + X- (aq) —> AgX (s)

• rate of reaction increases with increased number of alkyl substitutes • tertiary haloalkanes hydrolyse the fastest • mainly because tertiary haloalkanes react by 2-step mechanism, by primary haloalkanes is only 1 step • tertiary carbocation is more stable • tertiary carbocation and halide ion formed by C-X bond breaking by heterolytic fission • OH- ion attacks the carbocation

• general solvents • dry cleaning solvents • making polymers • flame retardants • regrigerants

CFCs are non-flammable and not very toxic compounds containing carbon with chlorine and fluorine atoms attached. They are chosen because of their low reactivity, high volatility and non-toxicity. • unreactive (stable) • volatile • non-toxic • non-flammable

• outer edge of stratosphere, 10-40 km above the Earth’s surface • consists of small amount of ozone, which absorbs biologically damaging UV radiation (UV-B rays) • UV radiation breaks down ozone into oxygen radicals (O), but then this and O2 reforms ozone (O3) • at a steady rate, the forward reaction = reverse reaction