(8.5 marks for correct structures, curly arrows, formal charges)
Part 6: MECHANISM
The following diagram shows the solution to the mechanistic question. Note that all the information applies to a single reaction sequence that has been completely described verbally. There is no need for extra reagents or extra steps etc. The curly arrows are drawn specifically to match the text in the question. The biggest problem students have is making sure they understand the language of chemistry. Most students have trouble because they can't draw the structures from the IUPAC names (that means they don't know their nomenclature well enough). Read the words carefully, and then make the curly arrows tell that same story. There is NO need for extra steps. Remember curly arrows go from electron rich to poor and to balance the formal charges at each step - errors on formal charges were common.
a.
(8.5 marks for correct structures, curly arrows, formal charges)
If you struggled with this part of the question, first draw the compounds whose names were provided, then think about the types of reactions (e.g. acid / base) and try to fill in the structures in the gaps, then finally add the required curly arrows to account for all the bonding changes.
In the image shown above note (a) how the charges balance at each step, (b) how each of the arrows start and end very close to the structures, (c) arrows go e rich to e poor and (d) arrows account for each of the bonding changes.
b. If H2O gives the alcohol, then an alcohol, ROH, will give an ether:
(1.5 marks for the product structure, 1.5 marks for a correct IUPAC name)
c. Deprotonation of the alcohol by the base for the alkoxide, a nucleophile which then reacts with the electrophilic C in the methyl iodide:
(1.5 marks for the product structure)
Common errors: