Effect of concentrations on SN2 reactions Part A. Changing substrate concentrati

Question

Effect of concentrations on SN2 reactions

Part A. Changing substrate concentrations. Take two small test tubes and add ~1 mL (one half pipet) of 15% NaI (acetone) to each test tube. Add 0.2 mL (200 µL, use the micropipette) of 1.0M 1-bromobutane to the first tube and 0.2 mL of 2.0M 1-bromobutane to the second tube. Try to do this at the same time (use both micropipettes) and observe if there is a difference in reaction time. Monitor the time it takes for any precipitation or cloudiness to appear. Record your observations and the time for precipitate to appear.

Part B. Changing nucleophile concentrations. Take two small test tubes and add ~1 mL (one half pipet) of 1.0M 1-bromobutane to each test tube. Add 0.2 mL (200 µL, use the micropipette) of 15% NaI (acetone) to the first tube and 0.2 mL of 7.5% NaI (acetone) to the second tube. Try to do this at the same time (use both micropipettes) and observe if there is a difference in reaction time.

QUESTION:Discuss what results are expected to be seen for this experiement based on what is known about SN2 reactions for part A and Part B.

Explanation / Answer

PART A.1 mL of 15% NaI+ o.2 mL of 1.0 M 1-bromobutane reaction is faster than 1ml of !5% NaI+0,2 mL of 2.0 M 1-bromobutane. Iodo butane formation is fast with 1.o M 1-bromobutane than 2.0M bromo butane.

PART B 1 mL of 1.0 1-bromobutane + 0.2 mL of 15% NaI is faster than 1 mL of 1.0 M 1-bromobutane +0.2 mL of 7.5% NaI. Iodobutane formation is fast with 15 % NaI than 7.5 % NaI.

In this case bromo nucleophile is replace by iodo nucleophile in SN2 fashion.

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