4. Propose a series of three pericyclic reactions that explain the following result Ja sous 250 °C

Hw.216.

Q5 (a) Justify the rate of reactions considering F as a Nu Alkyle halide Relative Rate Camments 200 0.02 79 200 920 100000

Choose the major product of the following reaction sequence

What is the major product when this reaction is done at relatively low temperatures? Br ∞∞∞∞ Br A HBr B Br C Br D

Hh.121.

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br. Draw the products obtained from each free-radical intermediate.

Tributyltin hydride (Bu3SnH) is used synthetically to reduce alkyl halides, replacing a halogen atom with hydrogen. Free-radical initiators promote this reaction, and free-radical inhibitors are known to slow or stop it. Your job is todevelop a mechanism,

The accepted mechanism for a rearrangement reaction is shown below. "Q Ph (1) (ii) Ph Ph HO™ fast Ph Ph HO O™ slow Ph aufae .Ar² LOH HO™ fast Draw a curly arrow mechanism for this transformation. Sketch an energy profile for this reaction, showing approximate relative energies for the reactants, intermediates, transition states, and products. HQ Ph (iii) When DO™ was used as the reagent, the rate of product formation was same as for HO™. Explain why this result shows that the third step is fast and cannot be rate-determining. Ph (iv) Write the predicted rate equation for this mechanism, and show how it was derived. (v) The starting diketone may have two different aryl groups, as shown below. Propose a ¹³℃ labelling experiment that would allow you to distinguish which of the two aryl groups had migrated in this situation. OH AR²0- Ar¹ C C

4. Rank the following reactions in terms of rate for an SN2 reaction (1 = fastest reaction). Are any of these reactions not possible? Br OH NaOH NaOH OMS NaOH NaOH