9701 · 31.1
Halogen compounds — FAQ
Frequently asked questions for 9701 Halogen compounds. Direct answers first, then deeper explanation — then practise with marking.
Why does using ethanol as a solvent favour elimination over substitution?
Ethanol is a less polar solvent than water. This makes the hydroxide ion () less well-solvated and therefore a stronger base. A stronger base is more likely to remove a proton (elimination) than to attack a carbon atom (substitution). Additionally, high temperature provides the activation energy needed for elimination.
If a halogenoarene has an alkyl side chain with a halogen on it, like (chloromethyl)benzene, is it reactive?
Yes, very. In (chloromethyl)benzene (), the chlorine atom is attached to a carbon that is not part of the benzene ring. This C-Cl bond behaves like a typical primary halogenoalkane bond. It is not strengthened by p-orbital overlap and will readily undergo nucleophilic substitution.
What are the modern replacements for CFCs?
Replacements include hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). HCFCs still contain chlorine but are less stable and break down in the lower atmosphere, having a smaller effect on the ozone layer. HFCs contain no chlorine and have zero ozone depletion potential, but they are potent greenhouse gases, so their use is also being phased down.