Question

studying SN1 reactions-oraganic chemistry

Prepare a 30 mL solution of 50% isopropyl alcohol solution by mixing together 15 mL isopropyl alcohol and 15 mL water). Divide the solution into three 10 mL portions, placing each one into a 50 mL flask. Add a drop of phenolphthalein indicator to each flask. Add 0.5 M NaOH drop by drop, with swirling, until each mixture is bright pink (this should only take a few drops).

Measuring the Effect of the Leaving Group on Reaction Rate

To the first flask, add 1 drop of the 2-bromo-2-methylpropane while swirling. Measure and record the time required for the solution to become colorless. To the second flask, add 1 drop of 2-chloro-2-methylpropane, with swirling. Measure and record the time required to become colorless.

Measuring the Effect of the Alkyl Group Structure on Reaction Rate

To the third mixture, add a drop of 2-bromopropane, with swirling. Measure and record the time required for the solution to become colorless. If the solution does not become colorless within 15 minutes, stop the reaction and record the time as > 15 min. Compare this time with the time it took for the first flask with 2-bromo-2-methylpropane to become colorless.

Measuring the effect of solvent polarity on reaction rate

Prepare 10 mL of a 40% mixture of isopropyl alcohol (4 mL isopropyl alcohol and 6 mL of water) and place into a 50 mL flask. Prepare another 10 mL of a 60 % mixture of isopropyl alcohol (6 mL isopropyl alcohol and 4 mL of water) in another 50 mL flask. Make sure these are labeled clearly. Add a drop of phenolphthalein indicator and then add 0.5 M NaOH drop by drop, with swirling, until each mixture is bright pink (this should only take a few drops). Add a drop of 2-bromo-2-methylpropane with swirling to each flask, measuring and recording the time required for each solution to become colorless.

1) the better leaving group:   Cl^-       or         Br^-         

2) weaker base:    Cl^-        or        Br^-

3) What is the relationship between the nature of the leaving group and basicity?

4) What compound is causing the indicator to change color?

5) Write out the complete mechanism for the conversion of 2-bromo-2-methylpropane to 2-methyl-2-propanol using curved arrows.

please show all work and provide explanation.

Answer 1

Br- is a better leaving group than Cl-. Why? Bigger size of bromo can stabilize negative charge better than Chloro 2 Br is the stronger acid and by that definition the weaker base. The F would be the strongest base, followed by the Cl, the Br, and lastly, the I Good leaving groups are weak bases. In order to understand the nature of the leaving group, it is important to first discuss factors that help determine whether a species will be a strong base or weak base. If you remember from general chemistry, a Lewis base is defined as a species that donates a pair of electrons to form a covalent bond. The factors that will determine whether a species wants to share its electrons or not include electronegativity, size, and resonance. 4 The Bromide ion generated in reaction is reacts with Phenophthalein and change colouless Phenophthalein to pink. And when reaction comes to end point, generation of Br- stop and color changes also stop Br 2-bromo-2-methylpropane NaOH OH +NaBr 2-methylpropan-2-ol