Module 4 Chapter 15 Flashcards
What can haloalkanes be classified as
primary, secondary and tertiary haloalkanes
What are primary haloalkanes
The carbon attached to group 7 atom has one alkyl group attached to
What are secondary haloalkanes
The carbon attached to group 7 atom has two alkyl group attached
What are tertiary haloalkanes
The carbon attached to the group 7 atom has three alkyl groups attached to
What is a property of the carbon halogen bond and why
Carbon - halogen bond
halogens are very electronegative
So the electron pair moves closer to the halogen, creating different charged regions
Making it polar
What is the halogen in the bond and the carbon in the bond
The halogen has a partial negative charge and the carbon is partially positively charged.
What can the carbon that is partially positively charged do
It can attract a species containing a lone pair of electrons
What are nucleophles
A species that can donate a lone pair of electrons, a group of atoms, that is attracted to an an electron deficient carbon atom and a new covalent bond forms.
What are some common nucleophiles
Hydroxide ions : OH-
water molecules - H2O
Ammonia molecules - NH3
What happens in the reaction with a nucleophile
The nucleophile replaces the halogen in a substitution reaction. And a new compound is formed with a different functional group.
What is the reaction when the nucleophile replaces a hydrogen atom called
Nucleophilic substitution
What do primary haloalkanes undergo lots of
They undergo lots of different nucleophilic substitution reactions to produce lots of different compounds.
What is a substitution reaction
A reaction in which one atom or group of atoms are replaced by another atom or groups of atoms.
What occurs in the hydrolysis of haloalkanes
The reaction involves water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule.
You get two products.
Halogens are replaced by the -OH group in a nucleophilic substitution reaction
What are the steps for the hydrolysis of haloalkanes
The nucleophile approaches the carbon attached to the halogen on the opposite side of the molecule from the halogen.
Draw the mechanism for the nucleophilic substitution of the hydroxide ion with the haloalkane
DRAW IT
How are haloalkanes converted to alcohols (conditions and reactants)
Using sodium hydroxide
Where they are heated under reflux to get a good yield.
What does the rate of hydrolysis depend on
It depends on the strength of carbon-halogen bonds in haloalkanes.
What is the order of strength of the carbon-halogen bonds
C-F»C-CL»C-I
As a result of the bond strengths what are the most reactive haloalkanes and the least reactive haloalkanes
Iodoalkanes react the fastest
Fluoroalkanes are unreactive as a large amount of energy is required to break the C-F bond.
How can the rate of reaction be followed
With a reaction in the presence of aqueous silver nitrate, where the halide ions produced react with silver ions to form a silver precipitate.
What is the nucleophile present in the reaction with aqueous silver nitrate
The water present.
Because haloalkanes are insoluble in water, what is the reaction done with
An ethanol solvent allowing the water and haloalkanes to mix and produce a single solution
What are the observations when the different haloalkanes undergo hydrolysis reactions in the presence of silver nitrate
1-chlorobutane A white precipitate forms very slowly
1-bromobutane A cream precipitate forms slowed than with 1-iodobutane but faster than with 1-chlorobutane
1-iodobutane A yellow precipitate forms rapidly
What are organohalogen compounds
Compounds that contain at least one halogen atom joined to the carbon chain
What are organohalogens used in and what is a feature of them
They are used in many pesticides and they are rarely found naturally and not broken down naturally.
What are the uses of organolhalogens
Solvents
Making polymers
Flame retardants
Refrigerators
Where is the ozone layer found
On the outer edge of the stratosphere, 10km-40km above the earth’s surface.
What is a feature of the gases in the ozone layer and what is the result
Not many gases exist there but the ones that do absorb the majority of UV radiation and as a result only a small amount of UV light gets to us.
What will happen as the ozone layer depletes
The more UV-B will make it to the surface leading to increased genetic damage in all living organisms and skin cancer in humans.
What occurs in the stratosphere
The ozone is continuously being made and broken down by UV
Very high energy UV breaks oxygen f to form oxygen radicals
And a steady state forms
What is a steady state
It is where the rate of formation of ozone is the same as the rate at which it is broken down.
What does human activity do to the equilibrium
It wrecks the equilibrium
What is equation for ozone being made and broken down
O2 + O <-> O3
What are CFCs and what are they used for
Chlorofluorocarbons
And they are used in refrigerators and in air-conditioning units.
Who researched how CFCs impact the atmosphere
Frank and Mario
What do CFCs remain stable until and what do the products do
They remain stable until the stratosphere where they break down, forming chlorine radicals.
These catalyse the breakdown of the ozone layer.
Due to the strength of the carbon halogen bond what occurs
The CFCs can spend a long time in the troposphere
As a result what do CFCs take a while to do and once they have done it what occurs
It can take them a while to reach the stratosphere, however once there the UV gives them the necessary energy to break the carbon-halogen bond in homolytic fission forming radicals.
Because C-CL has the lowest bond enthalpy what occurs
It is the first covalent bond to break
What is photodissociation
Where radiation starts the breakdown
What can other radicals do
Catalyse the breakdown of zone
How are nitrogen dioxide radicals formed and what can they do
They are formed naturally during a lightning trike and because of aircraft in the stratosphere. And they can cause the breakdown of ozone too.
What is the first propagation step for nitrogen dioxide
NO* + O2 —> NO2* + O2
NO2* + O —> NO* + O2
What is the overall equation for nitrogen dioxide catalysing the breakdown of ozone and what is it the same as and hence what does it show
O3 + O —> 2O2
The overall equation is the same as with the chlorine radicals showing that the radicals act as a catalyst for the process.
What is the first step when CF2Cl2 break down
CF2Cl2 —-> CF2Cl * + CL *
What are the two features of the chlorine radical that is formed
The chlorine radicals that forms is very reactive
It will react with an ozone molecule producing oxygen
What are the two propogation steps
CL * + O3 —-> ClO* + O2
ClO* + O —-> Cl * + O2
What is the overall equation for the reaction
O3 + O —> 2O2
What does propagation step 2 do
It regenerates a chlorine radical -breaks down another molecule of ozone in propogation step 1
Repeating cycle continuous chain reaction
1 CFC breaks 100,000 of ozone
