3.3.3 Halogenoalkanes Flashcards
What is a halogenoalkane?
An alkane with at least one halogen atom in place of a hydrogen atom
Why can halogenoalkanes undergo substitution reactions? (2)
The difference in electronegativity between carbon and the halogens forms polar bonds
The δ+ carbon is electron deficient so it is susceptible to attack from nucleophiles
What is a nucleophile?
An electron-pair donor
How are alcohols produced from halogenoalkanes? (2)
Nucleophilic substitution
Warm aqueous potassium/sodium hydroxide
How are nitriles produced from halogenoalkanes? (2)
Nucleophilic substitution
Ethanolic potassium cyanide
How are amines produced from halogenoalkanes? (3)
Nucleophilic substitution
Excess ethanolic ammonia
Sealed tube
What is the trend of reactivity in the halogens? (2)
Reactivity decided by carbon-halogen bond enthalpy
Going down group 7, bond strength decreases so rate of reaction increases
What does OH- act as in nucleophilic substitution?
Nucleophile
What does OH- act as in elimination?
Base
How are alkenes formed from halogenoalkanes? (3)
Elimination
Warm ethanolic KOH
Reflux
Why is ozone beneficial?
It absorbs ultraviolet radiation
What are CFCs? (2)
Chlorofluorocarbons
Halogenoalkane molecules where all the hydrogen atoms have been replaced by chlorine or fluorine atoms
How does ozone form naturally? (2)
UV light breaks down oxygen into two free radicals
An oxygen atom and an oxygen free radical react to form ozone
How does chlorine form in the upper atmosphere?
UV radiation breaks down C-Cl bonds in CFCs, forming chlorine free radicals
Why does chlorine catalyse the decomposition of ozone? (3)
Cl• + O3 > O2 + ClO•
ClO• + O3 > 2O2 + Cl•
The chlorine free radical is regenerated (catalyst) and attacks another ozone molecule
