These are the homework exercises to accompany the Textmap for McMurry's Organic Chemistry textbook.
Why is cysteine the only L amino acid with an R configuration at the alpha carbon?
Isoleucine has two stereogenic centers.
(a) Draw a Fischer projection of isoleucine.
(b) Draw a Fischer projection of an isoleucine diastereomer, and label each stereocenter as R or S.
The sulfur atom in the side chain causes the side chain to have higher priority than the other substituents.