Spring WS #2

Organic Chemistry CHM 252 and CHM 254L

CHM 252 Organic Chemistry II
Spring 2001
Workshop #2

1. Consider the reaction of the epoxide shown below under either acidic or basic conditions to yield the ring-opened product. Proceed by answering the following directed questions in order. Notice that the starting epoxide is the same, but the regiochemistry of reaction changes for basic versus acidic conditions.

First consider BASIC reaction conditions.

	Which reactive species is present in an aqueous solution of base?
	What is the charge on the reactive species? Characterize the reactive species as a Lewis acid or Lewis base (remember that Lewis acid is the same as electrophile and Lewis base is the same as nucleophile).
	Identify potential sites of reactivity in the epoxide molecule. Characterize these sites as Lewis acid or Lewis base.
	With the help of the curved arrows, show the movement of electrons that corresponds to the reaction between the epoxide molecule and your reactive species.
	Write the structure of the product formed by the reaction in #4.
	Is this intermediate (product) cyclic or open chain?
	What will the charge be on this intermediate? Is it a Lewis acid or Lewis base?
	Show with the help of curved arrows how the 1,2-diol product is formed from this intermediate.
	Identify all Lewis acids and bases in #8.
	Summarize all steps and identify structures for all reactants, intermediates, and products. Use curved arrows to show electron movements.
	Does the reaction follow an S_N1-type pathway or S_N2-type pathway?
	Is this reaction catalytic? Explain.

Now consider ACIDIC conditions:

	Which reactive species is present in an aqueous solution of acid?
	What is the charge on the reactive species? Characterize the reactive species as a Lewis acid or Lewis base (remember that Lewis acid is the same as electrophile and Lewis base is the same as nucleophile).
	Identify potential sites of reactivity in the epoxide molecule. Characterize these sites as Lewis acid or Lewis base.
	With the help of the curved arrows, show the movement of electrons that corresponds to the reaction between the epoxide molecule and your reactive species.
	Write the structure of the product formed by the reaction in #4.
	Is this intermediate (product) cyclic or open chain?
	What will the charge be on this intermediate? Is it a Lewis acid or Lewis base? Identify possible sites of reactivity in this intermediate.
	Identify a species in solution that could react with this intermediate.
	Show with the help of curved arrows how the species identified in #8 will react with the first intermediate.
	Write the structure of the second intermediate (product) formed in #9.
	What is the charge on this second intermediate?
	Show with the help of curved arrows how the 1,2-diol product is formed from the second intermediate.
	Identify all Lewis acids and bases in #12.
	Summarize all steps and identify structures for all reactants, intermediates, and products. Use curved arrows to show electron movements.
	Does the reaction follow an S_N1-type pathway or S_N2-type pathway?
	Is this reaction catalytic? Explain.