Alkanes Flashcards
What happens during nucleophilic substitution reactions
The delta + carbon does not have enough electrons and can be attacked by a nucleophile such as cyanide, hydroxide or ammonium ions
The nucleophile donates it’s lone pair of electrons to somewhere without enough electrons
Define nucleophile
An electron pair donor
A species with a lone pair of electrons that is able to form a coordinate bond
Explain the nucleophilic reaction, ‘hydrolysis of haloalkanes’ and state the conditions
Conditions: warm and aqueous
Reagent: NaOH or KOH
Reacting species: :OH-
Products: halogen and alcohol
Lone pair creates new bond between nucleophile and carbon
Carbon can only be bonded to four other atoms and so the bond between carbon and halogen breaks
The pair of electrons from the bond are taken by the halogen and become a lone pair
Define mechanism
A pathway that the reaction happens by
Explain the nucleophilic substitution reaction that forms a nitrile from a haloalkane and state the conditions
Conditions: warm and dissolved in ethanol
Reagent: potassium or sodium cyanide
Reaction species: cyanide ions
Products: nitrile with functional group C (triple bond) N and a halogen
Why is ethanol used as a solvent in the nucleophilic substitution reaction to form a nitrile
Ethanol used instead of water as OH ions could act as a competing nucleophile and produce some alcohol as product
What is a haloalkane
An Alkane with at lease one halogen atom in place of a hydrogen atom
Halogens are more electronegative than carbon
Therefore the carbon-halogen bond is polar, enabling it to undergo nucleophilic substitution
Explain the nucleophilic reaction to produce amines from haloalkanes and state the conditions
Conditions: warm haloalkane and excess ethanolic ammonia (ammonia dissolved in ethanol) which minimises further substitution
Reagent: ammonia ion
Must be in a sealed tube
Products: amine (NH2) and halogen reacts with ammonia
After the initial reaction, there is one extra hydrogen than needed therefore the ammonia ion acts as a base and removes the extra hydrogen
What happens during the chlorination of alkanes
C-C and C-H bonds in alkanes are non polar and therefore alkanes cannon react with polar things, water and haloalkanes
However they can react with non-polar substances such as oxygen or halogens if given enough energy
Halogens react with the alkanes in photochemical reactions, to form haloalkanes - free radical substitution
Define free radicals
Particles with an unpaired electron that are highly reactive
What are the conditions in a free radical substitution reaction
Ultra violet light
Reactions with fluorine take place in the dark, chlorine requires light and bromine & iodine need heat
What are chlorofluorocarbons
Haloalkane molecules where all the hydrogen atoms have been replaced by chlorine and fluorine atoms
How is the ozone layer formed
O2 + UV = 2O free radicals
O2 + O free radical = O3
How is the ozone layer being destroyed by CFCs
C-Cl bond in CFCs broken by UV light forming Cl free radical
This free radical is a homogenous catalyst and reacts with O3 to form the intermediate ClO free radical and an oxygen molecule
The free radical continues to react with O3 forming Cl free radicals which continue to react with O3
What happens during elimination reactions
A haloalkane forms an alkene
Warm haloalkane with hydroxide ion dissolved in ethanol
Hydroxide ion acts as a base and takes a proton from the carbon, H+, making water
Carbon has a spare pair of electrons and forms a double bond with another carbon atom
When the double bond is formed, the Br is removed
