Hi,
Thanks for the clarification.
For Passage 2 Q7, we invoke the concepts of crystallization for purification.
1. You would identify that you want to purify amphetamine, which has 1 chiral centre (the C with the N attached). Amphetamine is in a mix of 50/50 R and S, which we want to separate.
2. To purify amphetamine, we would react it with an enantiomerically pure material. In this passage we have used tartaric acid, which has 2 chiral centres.
3. When we form the two salts with tartaric acid (which has stereocentres RS), we will form two diastereomeric salts, which I will represent by their stereocentres
Salt 1: R(RS) and Salt 2: S(RS), where the bold comes from amphetamine and the (RS) comes from tartaric acid.
If we look at these salts, they have 3 stereocentres (eliminating A and B), and only one chiral centre that is opposite in configuration, coming from amphetamine (which eliminates C). This leaves us with D as the best answer.
For Passage 3 Q18
This is a tricky question. I would practice more to improve your assignment of chiral centres and seeing meso planes, but this is generally quite a tough question. What you can also do to help is eliminate answers - if you knew that you could eliminate C and D based on the fact that they are factually incorrect, you could improve your percent of guessing right to 50%, which is greater than other test takers might get on this question.
Unfortunately, there is not much else one can do but practice to identify meso compounds, but I keep in mind that this is a hard question - consider it a victory if you even eliminated to A and B.
Passage 3 Q 19
The Diels Alder Adduct is the product produced in the Diels Alder reaction - but I think this should be revised because it is not clear which adduct, or which carbon and you would normally be given that information in the passage. Thank you for pointing this out, we will fix this when we can.