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The second and third reactions form a meso product having a pseudoasymmetric carbon atom (C#3). These compounds are numbered from the end nearest the first R-configuration, and the sequence rule for the central carbon is R > S. The configuration at this stereogenic center is then given as r or s (lower case). The chiral products D & F are identical. Since the central carbon is not a stereogenic center (it has two identical substituents), it does not receive an R or S descriptor.