(a) Outline a Kiliani-Fischer synthesis of epimeric aldopentoses starting with D-(-)- erythrose (use Fischer projections).
(b) The two epimeric aldopentoses that one obtains are D-(-)-arabinose and D-(-)-ribose. Nitric acid oxidation of D-(-)-ribose yields an optically inactive aldaric acid, whereas similar oxidation of D-(-)-arabinose yields an optically active product. On the basis of this information alone, which Fischer projection represents D-(-)-arabinose and which represents D-(-)-ribose?