2.6 Halogenoalkanes Flashcards
Describe the elimination reaction forming propene
1 bromopropane + NaOH—— >propene + sodium bromide and water.
Describe an elimination reaction
Use an alkali to neutralise the acid of hydrogen halides.
The :OH- acts as a base and takes a proton (H+) from the carbon on the left to form water.
The left carbon now has a spare electron and so forms a double bond with the middle carbon.
To form this, the middle carbon has to let go of the halogen, forming a halogen ion eg. Br- ion.
What is the use of halogenoalkanes
Solvents
Anaesthetics
Refrigerants
What are the uses of halogenoalkanes as solvents
Halogenoalkanes are polar (Carbon is ∂+ and the halogen is more electronegative so ∂-) and they are non polar due to presence of alkyl chain. This means they can react with polar and non polar organic substances and used as solvents. Halogeno-alkanes are non flammable so can be used in dry cleaning clothes and other processes involving degreasing chloro-compounds
What are the uses of halogenoalkanes as an anaesthetic
Trichloromethane(CHCL3) is a modern anaesthetic and chloroform is old anaesthetic
HALOTHANE CF3CHBrCl is still in use today.
What are the uses of halogenoalkanes as a refrigerant
Small chain halogenalkane are gasses at room temp with permanent dipole interactions making their boiling points close to room temperature.Therefore liquids are easily evaporated or gasses are easily liquified at room temps, taking heat from their surroundings.
This makes them perfect in freezers and fridges. Non flammability and non toxicity as well as a suitable boiling temp is why halogenoalkanes r suitable
What are the environmental effects of CFCS
CFCs were used in household fridges but when they escape and rise to upper atmosphere a free radical substitution cause them to convert ozone to oxygen and making holes in ozone layer,
CFCs cause damage to earths ozone layer.
Damage to ozone layer means UV rays reach earth surface and cause skin cancer
What are some alternatives to CFCS
To avoid forming chlorine radicals we use alternatives that dont have chlorine and include alkanes and HFCSl since the only halogen is HFC is fluorine, radicals dont form when exposed to UV light.
What are the differences in bond strengths in C-Cl, C-H & C-F
C-Cl substitution involves breaking the carbon to halogen bond. This is the strongest C-Cl bond and is therefore the most difficult to break.
Nativity decreases the size of the halogen increases this means that the C-Cl is the polar with this carbon atom being more electronegative.
IODO>BROMO>CHLORO (fastest -slowest)
