(i) For the molecule below (cocaine hydrochloride salt), which is drawn in two different ways to...

 

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(i) For the molecule below (cocaine hydrochloride salt), which is drawn in two different ways to avoid ambiguity, identify all stereogenic centres. Using the Cahn-Ingold-Prelog rules, assign the configurational descriptor (R or S) to any two of the stereogenic centres, justifying your assignment in each case. -OCH OCH (ii) [10 marks] A solution of an enantiomerically pure sample of cocaine hydrochloride in chloroform (0.04 g/ml.) exhibits an optical rotation of-16.0 degrees. A solution of another sample in chloroform (at the same concentration) exhibits an optical rotation of-12.8 degrees, suggesting contamination with the other enantiomer of cocaine hydrochloride. If the lowered optical rotation is indeed due to the presence of the other enantiomer, calculate the ratio of enantiomers in the form X:Y (where X + Y = 100). 15 marks] (iii) Describe two methods by which the above enantiomerically impure sample of cocaine hydrochloride can be purified to deliver an enantiomerically pure sample of the major enantiomer. (iv) [5 marks] An enantiomerically pure sample of cocaine hydrochloride is subjected to a decarboxylation process, which transforms the molecule into compound A. Predict the optical rotation of A in chloroform (0.04 g/mL) and explain your answer. OCH H,C 15 marks] (i) For the molecule below (cocaine hydrochloride salt), which is drawn in two different ways to avoid ambiguity, identify all stereogenic centres. Using the Cahn-Ingold-Prelog rules, assign the configurational descriptor (R or S) to any two of the stereogenic centres, justifying your assignment in each case. -OCH OCH (ii) [10 marks] A solution of an enantiomerically pure sample of cocaine hydrochloride in chloroform (0.04 g/ml.) exhibits an optical rotation of-16.0 degrees. A solution of another sample in chloroform (at the same concentration) exhibits an optical rotation of-12.8 degrees, suggesting contamination with the other enantiomer of cocaine hydrochloride. If the lowered optical rotation is indeed due to the presence of the other enantiomer, calculate the ratio of enantiomers in the form X:Y (where X + Y = 100). 15 marks] (iii) Describe two methods by which the above enantiomerically impure sample of cocaine hydrochloride can be purified to deliver an enantiomerically pure sample of the major enantiomer. (iv) [5 marks] An enantiomerically pure sample of cocaine hydrochloride is subjected to a decarboxylation process, which transforms the molecule into compound A. Predict the optical rotation of A in chloroform (0.04 g/mL) and explain your answer. OCH H,C 15 marks]