Haloalkanes Flashcards
What is the general formula for Haloalkanes.
CnH2n+1X
Where X is a halogen
What is a primary haloalkane
2 hydrogens bonded to the carbon with the additional molecule ( the halogen).
What is a secondary haloalkane.
An alkanes which has one hydrogen bonded to the carbon with the halogen
What is a tertiary haloalkane.
An alkane with no hydrogens attaches to the carbon with the halogen.
What is the role of Ultra Violet light in creating haloalkanes.
UV light is an energy source which can break bonds in halogens therefore forming free radicals which are highly reactive.
What is a property of free radicals ?
They are highly reactive.
What is homolytic fission ?
Free radicals are formed when a covalent bond splits evenly and each atom gets one of the electrons. This occurs using UV light and is he initiation of creating haloalkanes.
What is it called when:
Free radicals are formed when a covalent bond splits evenly and each atom gets one of the electrons. This occurs using UV light and is he initiation of creating haloalkanes.
Hydrolytic fission
What are the required conditions of hydrolytic fission ?
UV light
Excess of whatever you want to create
For example excess of methane in chlorination of methane
What does excess reactant help with and how.
The excess of methane or whatever increases the chances of gaining the desired product which is wanted due to the high concentration.
What are the processes involved in creating free radical substances and explain them fully.
- Initiation where free radicals which are highly reactive are produced.
- Propagation where another molecule encounters a radical forming a new radical and a new molecule.
- Termination where 2 radicals react with eachother to form a molecule.
What does CFC stand for ?
Chlorofluorocarbons
What are the uses of CFCs
Coolants in fridges
Aerosol spray
Foam fire extinguishers
Dry cleaning solvents
When we’re CFCs developed and banned
1930s
1989
What is the ozone layer
An allotrope of oxygen has in the form O3 which is in high concentration and surrounds the planet absorbing a high proportion of the suns UV.
What are the risks of UV radiation.
Increased risk of sunburn
Risk of skin cancer
Accelerated ageing
Risk of cataracts
How is ozone made ?
Ozone is made naturally in the stratosphere. As oxygen molecules are bombarded by high energy UV light from the sun, the oxygen molecules break up and become oxygen radicals. These oxygen radicals then react with oxygen molecules.
Write the equation for production of ozone.
O2 - O0 + O0
2O0 + 2O2 - 2O3
Why and how do CFCs affect the ozone layer.
CFCs are very stable so can exist in the atmosphere long enough to reach the stratosphere. In the stratosphere they absorb UV and their covalent bonds are broken. Highly reactive radicals are then released. And then chain reactions cause production of oxygen. When these chain reactions occur , many ozone molecules are destroyed.
What is the equation for the initiation of creating CFCs.
CCl2F2 - CClF2 radical + Cl radical
What is the Montreal protocol.
In 1987
CFC usage and production was frozen and CFC products inside fridges were all removed.
Why were there still CFCs present in the atmosphere after the montreal protocol.
The very stable CFCs took a long time to deplete and be destroyed in the atmosphere.
Why is free radical substitution rarely used in industry ?
It is hard to target specific products and many isomers are created.
What alternatives were created after CFCs being banned ?
HCFCs
HFCs
What are HCFCs
Contain carbon, fluorine, chlorine and hydrogen. The addition of hydrogen makes them more reactive so the substance deplete and react in the troposphere before they reach the stratosphere.
What are HFCs
Hydroflurorcarbons
Hydrogen makes them more reactive so they deplete and react in the troposphere before reaching the stratosphere
Describe the bonding in haloalkanes.
The carbon - halogen bond is polar because halogens are Or- while carbon is Or+.
What are nucleophiles
A nucleophile is a negative ion or molecule able to donate a pair of electrons and take part in an organic reaction by attacking the electron deficient area of the other reactant.
How does nucleophilic substitution occur.
Negative nucleophiles attack the carbon in a carbon-halogen bond. The electron pair of the nucleophile are attracted towards the small positive charge on the carbon.
The electrons in the carbon - halogen bond are repelled by the nucleophile. The nucleophile bonds to the carbon and the carbon-hydrogen bonds are broken heterolytically. The 2 electrons move to the halogen and form a halogen ion.
What type of fission is nucleophilic substitution.
Heterolytically
Heterolytic fission
Write the overall equation and nuclear mechanism for the heterolytic fission (nucleophilic substitution) of a hydroxide ion with bromoethane.
In notes
What type of ions can nucleophilic substitution occur with ?
OH- hydroxide
CN- cyanide
NH3 ammonia
What are the required conditions of hydrolytic fission ?
UV light
Excess of whatever you want to create
For example excess of methane in chlorination of methane
What does excess reactant help with and how.
The excess of methane or whatever increases the chances of gaining the desired product which is wanted due to the high concentration.
What are the processes involved in creating free radical substances and explain them fully.
- Initiation where free radicals which are highly reactive are produced.
- Propagation where another molecule encounters a radical forming a new radical and a new molecule.
- Termination where 2 radicals react with eachother to form a molecule.
What is meant by the term ‘propagation step’?
A step in which radicals are used and formed.
Why is it difficult to oxidise 3-methylpentan-3-ol ?
It is a tertiary alcohol with no available hydrogen atom
What is the difference between heterolytic fission and homolytic fission ?
Heterolytic is when there is an uneven distribution of electrons. Both go to the halogen.
Homolytic fission has an even distribution of electrons.
What are the reagents for nucleophilic substitution?
An Aqueous solution usually of sodium or potassium.
What does ammonium reflux with and what product does this create ?
Reflexes with a water and alcohol solution under presssyre to create an amine.
What does hydroxide reflux with and what products does this produce ?
Reflux with water to create alcohols.
What does cyanide reflux with and what products does this create.
Reflux with ethanol to produce a nitrite which adds a carbon to the chain.
How does nucleophilic substitution with cyanide affect the haloalkane ?
The reflux of cyanide with ethanol adds an additional carbon to the chain when a nitrite is formed.
Why is nucleophilic substitution a substitution reaction ?
Halogen is substituted with the nucleophile.
Which is the leaving group is nucleophilic substitution?
The halogen
What is meant by the term stereoisomers ?
Compounds with the same structural formula.
Name a technique used to separate the different compounds in a liquid mixture.
Fractional distillation
What is meant by the term nucleophile ? (1 mark question)
An electron pair donor
Why is excess ammonia needed in a reaction with ammonia ?
More likely to react with ammonia
Minimises further substitution
What factors indicate an elimination reaction taking place ?
Hot temperatures
Tertiary haloalkanes
Ethanoic solvent solution
What factors indicate a substitution reaction ?
Warm temperatures
Primary haloalkanes
Aqueous water solvent
What are the products of an elimination reaction ?
Allene
Water
Halide ion
What base / nucleophile is used for elimination reactions ?
OH-
How does the OH- acts as a base in an elimination reaction ?
The OH- acts as a base and the nucleophile. It removes a H+ from the haloalkane and creates a halide ion.
Why are the products of eliminations reactions often a mixture.
They are often a mixture of alcohols from substitution and alkenes from elimination.
In what solution are elimination reactions favoured ?
Ethanoic solutions
In what solutions are substitution reactions favoured ?
Water (aqueous)
Draw the mechanism for when 2-chloropropane reacts with hot ethanoic KOH.
Notes
Draw the mechanism for when 2-bromobutane reacts with KOH.
In notes
Define free radical
Atoms with single unpaired electron
What is a photochemical reaction ?
A reaction induced by light
What is a chain reaction
A new reaction is generated for every starting reactivity species.
What is the difference between heterolytic fission and homolytic fission ?
Heterolytic is when there is an uneven distribution of electrons. Both go to the halogen.
Homolytic fission has an even distribution of electrons.
What are the reagents for nucleophilic substitution?
An Aqueous solution usually of sodium or potassium.
What does ammonium reflux with and what product does this create ?
Reflexes with a water and alcohol solution under presssyre to create an amine.
What does hydroxide reflux with and what products does this produce ?
Reflux with water to create alcohols.
What does cyanide reflux with and what products does this create.
Reflux with ethanol to produce a nitrite which adds a carbon to the chain.
How does nucleophilic substitution with cyanide affect the haloalkane ?
The reflux of cyanide with ethanol adds an additional carbon to the chain when a nitrite is formed.
Why is nucleophilic substitution a substitution reaction ?
Halogen is substituted with the nucleophile.
Which is the leaving group is nucleophilic substitution?
The halogen
What is meant by the term stereoisomers ?
Compounds with the same structural formula.
Name a technique used to separate the different compounds in a liquid mixture.
Fractional distillation
What is meant by the term nucleophile ? (1 mark question)
An electron pair donor
Why is excess ammonia needed in a reaction with ammonia ?
More likely to react with ammonia
Minimises further substitution
What is the difference between heterolytic fission and homolytic fission ?
Heterolytic is when there is an uneven distribution of electrons. Both go to the halogen.
Homolytic fission has an even distribution of electrons.
What are the reagents for nucleophilic substitution?
An Aqueous solution usually of sodium or potassium.
What does ammonium reflux with and what product does this create ?
Reflexes with a water and alcohol solution under presssyre to create an amine.
What does hydroxide reflux with and what products does this produce ?
Reflux with water to create alcohols.
What does cyanide reflux with and what products does this create.
Reflux with ethanol to produce a nitrite which adds a carbon to the chain.
How does nucleophilic substitution with cyanide affect the haloalkane ?
The reflux of cyanide with ethanol adds an additional carbon to the chain when a nitrite is formed.
Why is nucleophilic substitution a substitution reaction ?
Halogen is substituted with the nucleophile.
Which is the leaving group is nucleophilic substitution?
The halogen
What is bond elepathy ?
The minimum energy required to break a bond.
State the colour of the precipitate formed when iodide ions react with silver nitrate and write the simplest ionic equation for this.
Yellow
Ag+ + I- = AgI
