Mechanisms Flashcards
First stage in the formation of haloalkanes
Initiation
Second stage of the formation of haloalkanes
Propagation part 1 and 2
Final stage of formation of alkanes
Termination
What is required for initiation
Ultraviolet light
What is created during initiation
A halogen radical
What affects the composition of a radical
The electronegativity
Free radicals are
Highly reactive
What happens in initiation
A uv photon creates a free radical pair from a diatomic molecule
What happens in step one of propagation
The radical steals a hydrogen from the alkane creating a H-halogen molecule and an alkane with a radicalised carbon
What happens in step 2 of propagation
The radicalised carbon in the alkane strips a halogen of a diatomic molecule and forms a haloalkanes and a radicalised halogen
What is termination
When 2 radicals bond together to form a molecule with no radicals present
An example of a product created during termination
Cl2
An example of a free radical substitution
The destruction of Ozone
How are haloalkanes formed
Free radical substitution
Why are CFC’s so destructive
The chlorine radical
Nucleophilic substitution
When a Nucleophile substitutes itself with a halogen forming a halogen -1 ion
What do curly arrows represent
A movement of electrons
What do one headed curly arrows mean
Only one electron Moving
What does a full headed curly arrow mean
Movement of 2 electrons
What is a strong Nucleophile
Hydroxide ion
Conditions needed for nucleophilic substitution
A bond with an imbalance in charge (electronegativity)
A negatively charged ion or a molecule with lone pairs
How does nucleophilic substitution work step 1
A negatively charged ion or molecule with lone pairs is attracted to the mildly positively charged carbon
How does nucleophilic substitution work step 2
The mildly positively charged carbon donates 2 electrons to the halogen bond which displaces it
An example of a Nucleophilic substitution reaction
Halogenoalkanes with ammonia
First step in halogenoalkanes with ammonia
The lone pairs on the ammonia forms the bond to the mildly positively charged carbon
Step two of the reaction of halogenoalkanes with ammonia
The carbon donates electrons to the halogen which is ejected
The extra hydrogen is lost to balance charge and the hydrogen forms a dative bond with an excess ammonia
What is important for nucleophilic substitution
Lone pairs
What is a Nucleophile
It donates an electron pair to from a new covalent bond
What is homolytic fission
The splitting of covalent bonds into radicals where the radicals both take an electron
What is Heterolytic fission
Where a covalent bond is split and one of the 2 radicals takes both electrons and the other lacks one
What is a Electrophile
e- pair/lone pair acceptor
What is elimination
Where a molecule with lone pairs steals a hydrogen from a halogenoalkane forming an alkene
What are the conditions for elimination
A molecule with lone pairs and a haloalkane with a hydrogen diagonal from a halogen
Mechanism of bromoethene and sodium hydroxide step 1
The OH with lone pairs steal a hydrogen from a carbon
Mechanism of bromoethene and sodium hydroxide step 2
The electrons from tech stolen hydrogen pass to the carbon carbon bond turning it into a carbon double bond
Mechanism for bromoethene and sodium hydroxide step 3
The double bond displace the bromine turning it into a Br- minus ion
What conditions favour substitution
Cold OH- in water
What conditions favour elimination
Hot OH- in ethanol
Definition of addition
Reaction which increases number of substituents or convert double bonds to single bonds or where 2 molecules from one molecule
What is Electrophilic addition
Where a alkene becomes an alkane with extra stuff added
What are the conditions for Electrophilic addition
Needs a carbon carbon double bond and an Electrophile
Rough mechanism for Electrophilic addition
1.the Electrophile is attracted to the double bond
2.Electrophiles are positively charged and accept a pair of electrons from a double bond. The Electrophile may be positively charged
3.a positive ion is formed (a carbocation)
4. A negatively charged ion forms a Bond with the carbocation
Example of Electrophilic addition
The reaction of propane and sulfuric acid
What happens when ethene reacts with sulfuric acid step 1
The hydrogen is stolen by the double bond
What happens when ethene reacts with sulfuric acid step 2
The double bond opens up and bonds to the lone pair on the hydrogensulfate
What happens when you add water to the products of ethene and concentrated sulfuric acid
Ethanol is formed
How is ethanol formed from ethyl hydrogensulfate
The hydrogen from the water is stolen by the hydrogensulfate and the OH- bonds with the spare electrons and ethanol is formed
What is dehydration
When a water is produced and a functional groups of alcohol is removed
How does dehydration work
Either an aluminium oxide catalyst breaks bonds and forms water or a H+ ion causes an elimination reaction and a alkene is formed
What are the conditions for dehydration via aluminium oxide catalyst
600K
Al2O3 catalyst
What are the conditions for dehydration via elimination
Hot excess sulfuric acid
What is fermentation
When glucose is fermented into ethanol using organic processes
Conditions for the fermentation of ethanol from glucose
Yeast catalyst
Anaerobic conditions
310K
