organic chem; halogenoalkanes
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Halogenoalkanes
Are alkanes with 1 or more halogens attached to it
What is the boiling point trend for halogenoalkanes?
Increases down the group
Explain the boiling point trend of halogenoalkanes
• The no.of e- down the group increases • more e- means stronger VDWs forces between the molecules & so more energy is needed to overcome these forces • leads to be increasing down the group
Halogenoalkanes have a … bond and are attacked by …
…polar …nucleophiles
Why do halogenoalkanes have a polar bond?
As halogens are more electronegative than C so they pull the e- towards themselves
Nucleophile
Is a substance that is an e- pair donor
Examples of nucleophiles
• ammonia (NH3) • hydroxide ions (OH-) • cyanide ions (-CN)
Curly arrows show…
…the movement of e- pairs
Halogneoalkanes react with hydroxide ions through…
…nucleophilic substitution
What are the conditions of a nucleophilic substitution with hydroxide ions?
Warm aqueous sodium hydroxide (source of OH- ions) Carried out under reflux
Halogenoalkanes reacts with cyanide ions to make…
…nitriles
What are the conditions of nucleophilic substitution reaction with cyanide ions?
Warm ethanolic potassium cyanide (source of CN- ions) Carried out under reflux
Conditions of nucleophilic reaction with ammonia
Heat with ethanolic ammonia Must have excess ammonia
Products of nucleophilic substitution with ammonia
Amine and ammonium ions (NH4+)
Halogenoalkanes become more … , … the group
…reactive …down
What determines reactivity?
The bond strength/bond enthalpy determines the reactivity of haloalkanes — not bond polarity
Halogenoalkanes react with hydroxide ions through … using an …
…elimination …ethanol solvent
Conditions of elimination reaction with halogenoalkanes and hydroxide ions
Warm ethanolic sodium hydroxide (source of OH ions) Carried out under reflux
What is formed when reacting sodium hydroxide with a halogenoalkane when using ethanol as a solvent?
Alkene
What is formed when reacting sodium hydroxide with a halogenoalkane when using water as a solvent?
Alcohol
CFCs break down … in the atmosphere
…ozone (O3)
What are CFCs
They are molecules that have had all their H’s replaced by Cl and F — are stable molecules but are broken down by UV
What catalyses the break down of ozone?
Radicals
Why are C—Cl bonds broken easily?
As they have the lowest bond enthalpy