The phenomenon of configuration inversion in a chemical reaction was discovered in 1896 by Paul Walden (Section

Question:

The phenomenon of configuration inversion in a chemical reaction was discovered in 1896 by Paul Walden (Section 6.6). Walden's proof of configuration inversion was based on the following cycle:

(a) Basing your answer on the preceding problem, which reactions of the Walden cycle are likely to take place with overall inversion of configuration and which are likely to occur with overall retention of configuration?
(b) Malic acid with a negative optical rotation is now known to have the (S) configuration. What are the configurations of the other compounds in the Walden cycle?
(c) Walden also found that when (+)-malic acid is treated with thionyl chloride (rather than PCl5), the product of the reaction is (+)-chlorosuccinic acid. How can you explain this result?
(d) Assuming that the reaction of (-)-malic acid and thionyl chloride has the same stereochemistry, outline a Walden cycle based on the use of thionyl chloride instead of PCl5.