Substitution Reactions of Alkanes Flashcards Preview

Chemistry 6 - Organic Chemistry > Substitution Reactions of Alkanes > Flashcards

Flashcards in Substitution Reactions of Alkanes Deck (31)

why are alkanes considered to be fairly unreactive

- because they contain only carbon and hydrogen atoms
- and only have single bonds


why do alkane's single bonds make them unreactive

- they are not very polar
- so they dont undergo reactions with substances that are reactive
- such as acids, alkalis and reactive metals


what is a simple example of a substitution reaction between methane and chlorine gas

CH4 + Cl2 = CH3Cl + HCl


what is happening during the substitution reaction and what is it called

- one of the hydrogen atoms from methane have been replaced by a chlorine atom
- in this case, it would be called chlorination


what is the broader name given to substitution reactions using halogens



what does a mechanism do in chemistry

- it tries to explain the actual changes that happen during a reaction
- especially with the bonding between the atoms


what is a mechanism in chemistry (definition)

- a sequence of two or more steps
- each one represented by an equation
- that shows how a reaction takes place


what happens when you mix chlorine with methane at room temperature

no reaction occurs


what are the two conditions that need to be met in order for a reaction to occur

- there needs to be a sufficient rise in temperature
- or it needs to be exposed to ultraviolet radiation (sunlight)


what does the ultraviolet radiation affect

- the chlorine
- not the alkane (methane)


what does the ultraviolet light do to the chlroine

- it breaks the chlorine molecule (Cl2) into chlorine atoms


how are the outer electrons of this broken chlorine molecule distributed

- the bond in a chlorine molecule consists of a shared pair of electrons
- which are equally shared between the two atoms
- so when broken, each chlorine atoms takes one electron from the shared pair


what is this kind of bond breaking between chlorine molecules, for example, called

homolytic fission


what equation shows the chlorine molecule being broken down into two chlorine atoms and what is this step called

- Cl2 = Cl. + Cl. (notice the dots)
- this step is called initiation


what does the dot represent

an unpaired electron


if the dot represents and unpaired electron, what does that make and not make Cl.

- it doesnt make it an ion or a molecule
- but instead it is called a free radical


what is a free radical

- a species with an unpaired electron
- 'species' refers to any substance that can be represented by a formula
- which includes atoms, molecules, ions and radicals


how would chlorine radicals and methane molecules interact and why

- when they collide the chlorine radical will remove a hydrogen atom from the methane molecule
- this is because radicals are very reactive


what is the equation for this process and what is this step called

- Cl. + CH4 = CH3. + HCl
- this called propagation (1)


what would the newly created molecular radical now react with, along with this formula

- it would react with chlorine molecules to produce chlorine radicals
- CH3. + Cl2 = CH3Cl + Cl.


what is that step called

propagation (2)


why are the two steps called propagation

- because both equations involve one radical reacting with molecule
- which produces one radical and one molecule


what is the overall product when the two propagation steps are combined

CH4 = CH3Cl


what is the last reaction that can take place

- two radicals colliding and reacting with each other
- to form a stable molecule


why is a molecule produced

the two unpaired electrons (one from each radical) are shared to form a covelant bond


what are the three different possibilities of two radicals reacting together in this chlorine and methane reaction

- Cl. + Cl. = Cl2
- Cl. + CH3. = CH3Cl
- CH3. + CH3. = C2H6


what is the name of this final step to the reaction and what does it mean

- termination
- meaning that the sequence of reactions come to an end
- because two reactive species are converted into one unreactive species


when chlorine reacts with a methane molecule in a substitution reaction to form chloromethane, is that the end of the reaction or can that new molecule continue to react with chlorine

- it can continue to react with more chlorine molecules
- by displacing the remaining hydrogen atoms
- and making the molecule more 'saturated' with chlorine atoms


what are the 3 following products that could be produced when reacting chloromethane with chlorine

- dichloromethane
- trichloromethane
- tetrachloromethane


what are the equations for the production of those three products

- CH3Cl + Cl2 = CH2Cl2 + HCl
- CH2Cl2 + Cl2 = CHCl3 + HCl
- CHCl3 + Cl2 = CCl4 + HCl


why isnt this reaction between chlorine and methane not a good method for the preparation of chloromethane

- the yield will be low because of these further reactions
- and the products would have to be separated