3.3 Haloalkanes Flashcards
Are haloalkanes or alkanes more reactive?
Haloalkanes are more reactive than alkanes.
What uses of haloalkanes are there?
Many uses e.g refrigerators, solvents and in pharmaceuticals.
Can all haloalkanes be used without limitations?
The use of haloalkanes has, had to be restricted.
Name one restricted group of haloalkanes and why it is restricted.
One restricted group are CFCs due to their affect on the atmosphere.
What type of bonds do haloalkanes contain?
Haloalkanes contain polar bonds.
What are the nucleophiles for substitution reactions?
The nucleophiles for the substitution reactions are OH–, CN– and NH3.
In elimination what do reagents act as?
A base
In nucleophilic substitution what do reagents act as?
A nucleophile
How does bond enthalpy affect the nucleophilic substitution reaction?
The higher the bond enthalpy of the bond between the carbon-halogen, the slower the nucleophilic substitution reaction.
What must haloalkanes contain?
Haloalkanes must contain at least one halogen which replaces a hydrogen atom.
Name 4 Mechanisms
Free radical substitution, electrophilic addition, nucleophilic substitution and elimination
What causes C-Cl bonds in CFCs to break (releasing Cl atoms) when in the atmosphere?
UV light
What effect do Cl atoms have on the atmosphere?
They catalyse the decomposition of ozone, contributing to holes in the ozone layer
Describe the conditions for elimination with OH-
Concentrated NaOH, high temperature, pure ethanol for the solvent and the use of a tertiary haloalkane
Describe the conditions for substitution with OH-
Use a primary haloalkane, dilute NaOH, low temperature (warm)
What is the name of the product formed in a substitution reaction with cyanide ions?
Nitrile
What is different about the carbon chain of the product when compared to the initial carbon chain in a substitution reaction with CN- ions?
The product has one more carbon in the chain
What are the stages of a mechanism?
Initiation, propagation and termination
What is formed in an elimination reaction with OH- ions?
An alkene
What is formed in a substitution reaction with OH- ions?
An alcohol
What happens in an elimination reaction?
one hydrogen atom and one halogen atom are removed from neighbouring carbon atoms in the molecules and a double bond forms between the two carbons
What conditions are required for substitution reactions?
Base: low concentration of OH- ions Solvent: water + ethanol Temperature: low
What conditions are required for elimination reactions?
Base: high concentration of OH- ions Solvent: ethanol Temperature: high
Which type of reaction (substitution or elimination) favours primary/ secondary/ tertiary haloalkanes?
-Primary favours substitution -Secondary favours neither -Tertiary favours elimination
