Mechanisms Flashcards
Addition reactions
Two or more molecules react together to form a single molecule
Ethene + Bromine molecule
1,2 dibromoethane
Ethene + Chlorine molecule
1,2 dichloroethane
Ethene + hydrogen chloride
Chloroethane
Ethene +H2O
Ethanol
Function of 1,2 dibromoethane
Used as fumingant for treating logs against termites and beetles
Function of 1,2 dichloroethane
To manufacture chloroethane
To make polyvinyl chloride
Function of chloroethane
Used in dentistry to identify a ‘dead tooth’
Function of ethanol
Used as an industrial solvent and fuel
Step 1: Mechanism of the Reaction between Ethene and Bromine
Br molecule become polarised as they come closer to the carbon carbon double bond of an ethene molecule. (One molecule is delta positive and the other is delta neg)This is because its a region of high concentration of negative charge.
Step 2: Mechanism of the Reaction Between Ethene and Bromine
The polarization becomes so great it splits the Br molecule with one becoming positively charged and the other becoming negatively charged. This is called a heterolytic fission. This also create free radical bromine
Step 3: Mechanisms of the Reaction Between Ethene and Bromine
The Br+ will want to regain its two electrons by attacking the ethene molecule carbon carbon double bond and creating a covalent bond with one of the carbon atoms. This leaves positvely charged carbon atom and its now called a carbonium ion.
Step 4: Mechanisms of the Reaction Between Ethene and Bromine
The Br- ion attacks the carbonium ion this is called the ion addition. This results in the prodution of 1,2 dibromoethane
Evidence for the mechanism of the reaction between Ethene and Bromine
When ethene reacts with bromine in water that contains sodium chloride in solution 1-bromo-2chloroethane and 2-bromoerhanol is produced this shows carbonium ion is present
Elimination Reaction
A small moleule os removed from a larger molecule to leave a double bond in the larger molecule
Example of an elimination reaction
Ethanol -Al2O3-> Ethene + H2O
Substitution reaction
A chemical reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms
Mechanism
The detailed step by step description of how the overall reactoon occurs
Step 1: Mechanisms of the Reaction between Methane and Chlorine
With the presence of a UV light its energy is enough to break the weak van der waals forces between these molecules. This created chlorine free radicals. Since the electrons are equally shared after the split its called a homolytic fission
Step 2: Mechanisms of the reaction Between Methane and Chlorine
One of the chlorine free radicals attacks the methane molecule to form a methyl free radical. Since the chlorine free radical has produced a methyl free radical this is called propagation
Step 3: Mechanisms of the Reaction Between Methane and Chlorine
The other chlorine free radical attacks the methyl free radical and forms chloromethane. The chlorine atoms produced in step 3 can cause a chain reaction
Chain reaction
A reaction that continues on and on because a product from one step of the reaction is a reactant for another step of the reaction
Step 4: Mechanisms of the Reaction Between Ethene and Chlorine
In order to stop the chain reactions two chlorine free radicals can combine to make Chlorine molecule. A chlorine free radical and methyl free radical can combine to make chloromethane. Two methyl free radicals combine to make ethane
Evidence of the Reaction Between Ethene and Chlorine
Reaction takes place in UV light. Suggests Cl2 has broken to make chlorine free radical.
Ethane is a product. Only evident if two methyl free radicals are present
Adding free radicals like tetramethyl lead speeds up a reaction. Only free radicals reacting to other radicals encourages chain reaction
