1. Reaction Pathways

2. Syllabus Statement
Deduce reaction pathways given the starting material and the product.
(This is the same for HL and SL – HL just have to know MORE pathways!)

3. Sometimes a product can’t be made directly from the given starting material.
E.g. convert 1-iodopropane into propanal
This can’t be done directly – we have no mechanism for converting a haloalkane into an aldehyde.

4. It is usually easier to approach the problem backwards!
What substance CAN be made into an aldehyde?
We only know 1.
A primary alcohol

5. So we know our pathway ends . . .
Alcohol  aldehyde
Or more specifically . . .
Propan-1-ol + [O] propanal + H2O
What conditions would we use?
Distil with acidified pot dichromate(VI)

6. So can we make a primary alcohol from 1-iodopropane?
Yes!
Hydrolyse with aqueous OH-

7. So the full reaction mechanism is . . .
1-iodopropane + OH-  1-propanol +I-
1-propanol +[O]  propanal + H2O

8. Another example . . .
Give a pathway for producing butanone from but-2-ene.
The only way of making a ketone is from a secondary alcohol . . .
So we must make butan-2-ol

9. We can make butan-2-ol from but-2-ene by reacting the alkene with water. (addition reaction)
So the full mechanism
But-2-ene + H2O  butan-2-ol
(this should have H+ catalyst written above the arrow, but I can’t do that on PowerPoint)
Butan-2-ol + [O]  butanone
(reflux with hot acidified dichromate(VI)

10. This can be summarised for SL

11. Diagram of common organic reactions. 11

12. And the additional bits for HL . . .

13. Diagram of common organic reactions13

14. I find these summaries confusing.
And they don’t have the conditions needed for the reactions.
So I would like you to produce your own summary in the form of a table.

15. Starting material
Finishing material
Reagent and conditions
Mechanism required
Alkane
halogenoalkane
Alkane + UV light
Yes
dihalogenoalkane