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Consider parallel first-order reactions A -> B (k1 = 6.93 * 10⁻¹ min⁻¹) and A -> C (k2 = 13.86 * 10⁻¹ min⁻¹). A, B and C are all optically active, with specific rotations per unit concentration of +60 deg, -72 deg and +42 deg respectively. The initial concentration of A is 2 M. Which statement is correct?
- Solution will be optically active and dextrorotatory after very long time
- Solution will be optically active and levorotatory after very long time
- Half life of reaction is 15 min
- After 75% conversion of A into B and C angle of rotation of solution will be 36 deg
Correct answer: Solution will be optically active and dextrorotatory after very long time
Solution
At t = infinity, A (2 M) splits into B = 2*(1/3) and C = 2*(2/3); net rotation = (2/3)(-72) + (4/3)(42) = -48 + 56 = +8 deg, which is positive (dextrorotatory).
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