15. Haloalkanes
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What is an example of nucleophilic substitution of haloalkanes?
Hydrolysis
What happens during hydrolysis?
The halogen is replaced by an -OH group
What condition is required to start hydrolysis of haloalkane?
Heat under reflux
What solutions are used to measure the rate of hydrolysis of haloalkanes by water?
• aqueous silver nitrate (AgNO3) • ethanol
What are the factors that affect the rate of hydrolysis? Which one is the main factor?
1. bond strength between carbon and halogen (outer shell) 2. polarity
What is the product when haloalkane is heated under reflux and reacts with sodium/potassium hydroxide (NaOH/KOH) ?
Alcohol (+metal halide)
What is the product when haloalkane is heated under reflux and reacts with sodium/potassium cyanide (NaCN/KCN) in ethanol?
Nitrile (+metal halide)
What is the functional group of nitrile? How to name nitrile?
C≡N. Add -nitrile after the alkane, eg. propanenitrile.
how many bonds does nitrogen form?
3
What is the product when haloalkane is heated under reflux and reacts with ammonia (NH3) in ethanol?
Amine (+hydrogen halide)
What is the functional group of amine? How to name amine?
NH2. Replace the -ane with -yl and add -amine after it, eg. propylamine.
What is a nucleophile?
An electron pair donor / a species that is often negatively charged and seeks out positively charged area.
What are the examples of nucleophiles?
• hydroxide ions (:OH-) • water (H2O:) • ammonia (:NH3) • cyanide ions (:CN-) • ethyl (CH2CH3)
Which carbon–halogen bond is the strongest? How is its rate of hydrolysis? Why?
C-Cl. It reacts the slowest because chlorine’s outer shell is the closest to the nucleus. This means that C-Cl bonds have the lowest bond enthalpy. Permanent dipole increases intermolecular forces, so the melting point is higher.
What conditions and solutions are required to produce alcohol when hydrolysing haloalkane?
• NaOH/KOH (sodium/potassium hydroxide) • reflux
What conditions and solutions are required to produce nitrile when hydrolysing haloalkane?
• NaCN/KCN (sodium/potassium cyanide) • ethanol • reflux
What conditions and solutions are required to produce amine when hydrolysing haloalkane?
• NH3 (ammonia) • ethanol • reflux
What are organohalogen molecules?
Compounds that contain at least one halogen joined to a carbon.
What are organohalogen molecules used as?
• solvent • making polymers • dry cleaning agents • flame retardants (阻燃劑) • refrigerants • pesticides
Where is the ozone layer found?
On the outer edge of the stratosphere
How far is ozone above Earth’s surface?
Between 10 to 40 km
What is the formula of ozone?
O3
How does ozone form?
By a reaction involves O2 and an oxygen radical, which requires UV light. (O2 + O ⇌ O3)
What does ozone do?
It absorbs most of the biologically damaging UV radiation from the sun called UV-B.