Reactions involving radicals - OZ Flashcards
What are the ways in which a covalent bond can be broken
hetrolytics fission and homolytic fission
What happens during heterolytic fission
each fragment gets a different outcome i.e. one fragment gets both electrons from the bond and the other gets no electron - this creates ions
What happens during homolytic fission
each fragment gets the same outcome i.e. each fragment gets one electron from the bond - creates radicals
Radicals definition
species with an unpaired electron
Diagram when the covalent bond breaks during heterolytic fission
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSYxybnGZ9EcNlW-Rm6ZbbX58CxlxYa3Nn6fw&s
Diagram when the covalent bond breaks during homolytic fission
https://study.com/cimages/multimages/16/834dd3d3-018a-41fc-a380-fc69c5fdbbfa_homolytic_fission.jpg
What are single headed curly arrows used for
to show that only one electron has moved
What is required for homolytic fission to occur
uv radiation
What reaction is an alkane and halogen
chain reaction
What happens in the dark of a alkane and halogen reaction
nothing
What happens in uv of a alkane and halogen reaction
explosion
What is produced when the halogen (chlorine) and alkane (methane) react
CH3Cl + HCl
WHat is the mechanism of the reaction of halogens and alkanes
radical substitution
Name the 3 stages of the reaction of halogens and alkanes
- Initiation
- Propagation
- Termination
Initiation stage during reaction of halogens and alkanes - What happens
radicals are first produced, these radicals are vey reactive
Propagation stage during reaction of halogens and alkanes - What happens
one of the radicals reacts but a new one is given, the new radical will also react so these steps continue the chain reaction
Termination stage during reaction of halogens and alkanes - What happens
where 2 radicals combine giving no new radicals, this step stops the chain reaction
Initiation stage during reaction of halogens and alkanes - How does this occur and what does it cause
the uv light provides the energy needed for the halogens X-X bond in some of the X2 molecules to break (homolytic fission) - this is photodissociation
Diagram of initiation stage during reaction of halogens and alkanes using chlorine/methane
https://homework.study.com/cimages/multimages/16/propagation7890035615492487370.png
(only first step)
What happens to chlorine/methane in the initiation stage during reaction of halogens and alkanes
the covalent bond breaks giving each chlorine one electron so it produces 2 chlorine radicals (which are just an ordinary chlorine atom with its 7 outer shell electrons but with a dot to show its unpaired electron - that is what makes it so reactive)
Propagation stage during reaction of halogens and alkanes - What does it cause using chlorine/methane
- First the chlorine radical takes an H atom form the methane molecule leaving a methyl radical which itself is extreemly reactive. It reacts by taking a Cl atoms from one of the many Cl2 molecules around. This regenerates a Cl* radical, which will atttack another methane molecule, so these 2 propagation steps happen over and over again rapidly many thousands of time (explosion) continuing the chain reaction
Diagram of propagation stage during reaction of halogens and alkanes using chlorine/methane
https://d10lpgp6xz60nq.cloudfront.net/physics_images/BLJ_MSC_ORG_CHE_JEE_C04A_E01_038_S01.png
(Step 2)
Diagram of termination stage during reaction of halogens and alkanes using chlorine/methane
https://chem.libretexts.org/@api/deki/files/464315/mechanisms_for_termination_steps_of_radical_halogenation.svg?revision=1&size=bestfit&width=386&height=265
How does the chain reaction stop during the reaction of halogens and alkanes
if any 2 radicals collide they will react together but this is rare as the conc of radicals is always relatively low, but will happen randomly
Is activation energy for termination during reactions of halogens and alkanes high or low and why
very low because no bonds need breaking only bond making in involved
What else could be produced after a while during the reaction of chlorine and methane and why
CH2Cl2, CHCl3, CCl4 as further substitution will take place especially with excess Cl2
Why aren’t radical reactions used very often
they give mixtures of the desired product and further substituted products. They are very hard to control. So another method is usually found
