write substitution reactions for alkanes?
Answers
Answered by
0
Halogenation of alkanes:
Alkanes and halogens react in conditions of ultraviolet radiation or at a temperature of about 300°C.
For example;
CH4+Cl2→CH3Cl+HCl
This reaction is radical substitution.
When we are talking about the mechanisms of a reaction, we are looking at how a reaction takes place showing step by step the bonds which break and the new bonds which form.
And when we are showing this, what we are actually showing is the movement of electrons. We use a curly arrow to show the movement of a pair of electrons and a curly arrow with only half an arrow-head to show the movement of just oneelectron.
Some mechanisms involve homolyticbond breaking (homolytic fission) and some involve heterolytic bond breaking (fission).
Homolytic fission is a type of bond breaking which produces free radicals(reactive particles with unpaired electrons. The symbol for a free radical generally shows the unpaired electron as a dot. For example Cl•). In homolytic fission, a covalent bond breaks and of the two electrons that make up that bond, one electron goes to each atom that was in the bond. This means that two radicals are formed.
Heterolytic fission is a type of bond breaking which produces ionic intermediates in reactions (atoms, molecules, ions or free radicals which do not appear in the balanced equation but which are formed during one step of a reaction, then used up in the next step.). In heterolytic fission, a covalent bond breaks so that one of the atoms joined by the bond takes both of the shared pair of electrons while the other is left with none.
We are going to look at free-radical substitution, this is the reaction of an alkane in sunlight in a free-radical chain reaction.
Free-radical chain reactions involve three stages:
Initiation– the step which produces free radicals
Propagation– steps giving products and more free radicals
Termination– steps which remove free radicals by turning them into molecules
For example:
In the reaction of methane with chlorine, the initiation reaction has to be Cl2→2Cl•
The bond between the two chlorines is broken by UV light. The pair of electrons in the bond between the chlorines split up and one goes to each chlorine in homolytic fission, therefore producing two free radicals.
Propagation:
CH4+Cl•→CH3•+HCl
CH3•+Cl2→CH3Cl+Cl•
Termination:
2Cl•→Cl2
2CH3•→C2H6
CH3•+Cl•→CH3Cl
etc.
Alkanes and halogens react in conditions of ultraviolet radiation or at a temperature of about 300°C.
For example;
CH4+Cl2→CH3Cl+HCl
This reaction is radical substitution.
When we are talking about the mechanisms of a reaction, we are looking at how a reaction takes place showing step by step the bonds which break and the new bonds which form.
And when we are showing this, what we are actually showing is the movement of electrons. We use a curly arrow to show the movement of a pair of electrons and a curly arrow with only half an arrow-head to show the movement of just oneelectron.
Some mechanisms involve homolyticbond breaking (homolytic fission) and some involve heterolytic bond breaking (fission).
Homolytic fission is a type of bond breaking which produces free radicals(reactive particles with unpaired electrons. The symbol for a free radical generally shows the unpaired electron as a dot. For example Cl•). In homolytic fission, a covalent bond breaks and of the two electrons that make up that bond, one electron goes to each atom that was in the bond. This means that two radicals are formed.
Heterolytic fission is a type of bond breaking which produces ionic intermediates in reactions (atoms, molecules, ions or free radicals which do not appear in the balanced equation but which are formed during one step of a reaction, then used up in the next step.). In heterolytic fission, a covalent bond breaks so that one of the atoms joined by the bond takes both of the shared pair of electrons while the other is left with none.
We are going to look at free-radical substitution, this is the reaction of an alkane in sunlight in a free-radical chain reaction.
Free-radical chain reactions involve three stages:
Initiation– the step which produces free radicals
Propagation– steps giving products and more free radicals
Termination– steps which remove free radicals by turning them into molecules
For example:
In the reaction of methane with chlorine, the initiation reaction has to be Cl2→2Cl•
The bond between the two chlorines is broken by UV light. The pair of electrons in the bond between the chlorines split up and one goes to each chlorine in homolytic fission, therefore producing two free radicals.
Propagation:
CH4+Cl•→CH3•+HCl
CH3•+Cl2→CH3Cl+Cl•
Termination:
2Cl•→Cl2
2CH3•→C2H6
CH3•+Cl•→CH3Cl
etc.
Similar questions