5. "Tartaric acid" is the common name given to any of the straight-chain four carbon dicarboxylic acids with hydroxyl substituents at the middle two carbons. "L-tartaric acid" is the form of tartaric acid which has the specific structure shown on the right. It occurs in the juice of fermented grapes; it has a value for [ α] οφ+ 11.98 ο ατ25 ο Χ . H OH CO 2 H HO H HO 2 C a) The "L" in "L-tartaric acid" is used to specify (by comparison to L-glyceraldehyde) its absolute configuration in 3-dimensional space. Provide the absolute configuration of the chiral carbons in l-tartaric acid using the Cahn-Ingold-Prelog (or R/S) system. (5 points) c) Imagine you have three beakers (beakers X, Y, and Z), each containing an aqueous solution of tartaric acid and tartaric acid only. The optical rotation of each solution is measured, and each gives a reading of zero. i) How could you determine for sure that the value for a was 0 o , not +360 o or -360 o ? (4 points)
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