9701 MCQ Solution 61

04:14 organic 0 Comments

Question 61: [Organic > Introductory Organic]

The isomers, citric acid and isocitric acid, are intermediates in the Krebs cycle of the oxidation of glucose in living cells.

How many chiral centres does each acid possess?

Reference: Past Exam Paper –June 2003 Paper 1 Q21

Solution 61:

Answer: B.

All carbon atoms in CO₂H group are not chiral. All carbon atoms in CH₂ groups are not chiral. In citric acid the only remaining left-middle carbon atom is also not chiral since the bottom group exactly matches the top, cancelling out options C and D. In isocitric acid the left-middle carbon atom is chiral since the groups attached to it are: H, CO₂H, CH₂CO₂H and C(OH)CO₂H, which are all different. The bottom-left carbon atom is also chiral since the groups attached to it are: H, OH, CO₂H and the remaining top, which are also all different. Thus the correct answer is option B.