Laying out a 10-mark mechanism answer
A mechanism question is marked on whether the examiner can see each step. Put the working into the diagram and keep the sentences for what the diagram cannot say.
Start with the scheme
Write the overall reaction in one line, with reagents and conditions over the arrow.
Draw the mechanism and label it
- Curved arrows from the electron source to the electron sink.
- The intermediate, named: carbocation, carbanion, radical or tetrahedral intermediate.
- The slow step, marked as rate-determining.
- The stereochemistry at any centre that changes.
Add three or four lines
State the rate law or order, the reason for the regiochemistry or stereochemistry, and one piece of evidence if the question asks why. Underline the terms the examiner is looking for.
An example
For the hydrolysis of tert-butyl bromide, draw an energy profile with two transition states and the carbocation between them, and mark the first step as slow. Then write rate = k[(CH₃)₃CBr] and note that the planar carbocation can be attacked from either face. That is a complete 10-mark answer in half a page.