Halogenoalkanes Flashcards
(17 cards)
Why are haloalkanes polar
Halogens are very electronegative so in the C-Halogen bond the carbon atom has a slight positive charge and the halogen a slight negative
Why do haloalkanes have higher boiling points than the equivalent alkane
Alkanes are non-polar so only have van der Waals forces,
Haloalkanes also have permanent dipole-dipole interactions which are stronger than van der Waals
Why does the boiling point increase as you go down group 7 of haloalkanes
Because van der Waals forces are larger when there are more electrons
Are haloalkanes soluble in water
No because they can’t form hydrogen bonds
What is a nucleophile
Something with a lone pair of electrons that are attracted to an electron-deficient carbon atom
A covalent bond forms between the carbon atom and the nucleophile
What are the conditions for the hydrolysis of haloalkanes (nucleophilic substitution)
In an aqueous solution of hydroxide ions
Ethanol- to solubilise the haloalkane so it can react
Heat under reflux- increases the rate of reaction
Why is ammonia a nucleophile
NH3, there is a lone pair of electrons on the N
What does ozone do in the stratosphere
It breaks an oxygen molecule into two oxygen radicals
How is ozone formed
An oxygen radical reacts with an oxygen molecule
Why doesn’t the level of ozone constantly increase
UV can break ozone back into a radical and a molecule
What is a chloroflurocarbon
A very stable haloalkane with the formula CFCl3
What happens to CFCs in the stratosphere
UV light causes a carbon chlorine bond to break creating a chlorine radical (very reactive)
What happens in propagation step 1
A chlorine radical reacts with a molecule of ozone, producing an oxygen molecule and a chlorine monoxide radical
What happens in propagation step 2
The chlorine monoxide radical reacts with an oxygen radical, producing an oxygen molecule and a chlorine radical (which can go back and trigger step 1)
Describe the nucleophilic substitution of a haloalkane with ammonia
The lone electron pair on the ammonia nitrogen is attracted to the slightly positive charge on the carbon of the carbon-halogen bond,
The nitrogen forms a covalent bond with the haloalkane,
The halogen is removed through heterolytic fission
Another ammonia group is attracted to the positive hydrogen that is bonded to the nitrogen so it takes it
NH4 bonds with the halogen ion
An amine and an ammonium salt are formed
Describe the reaction between cyanide and a haloalkane
The lone electron pair on the cyanide is attracted to the slightly positive carbon that is bonded to the halogen
A covalent bond forms with the cyanide and the carbon, creating a nitrile
The halogen is removed through heterolytic fission creating a halogen ion
Describe the elimination of haloalkanes to form an alkene
HO: from potassium hydroxide is attracted to a hydrogen on the haloalkane
It removes it from the haloalkane, forming a covalent bond and water
The bond that was between the carbon and hydrogen moves to the carbon next to it (double bond), the halogen on that carbon is then removed and bonds with the potassium from the start
