CHEM 205 Worksheet (WS5)

56 Points Total

Key Topics: Nucleophilic Substitution Reactions (SN1 or SN2, Reactions using PBr3, SOCl2, or TsCl.

1. Consider the scheme below then complete the following parts.

(a) (4pts) The stereochemistry expected for Product A has not been shown clearly. Using the template provided in the box above, complete the Fischer projection of Product A to show the stereochemistry of this product clearly.

(b) (12pts) Based on the following information, complete the Fischer projections for Product B, Product C, and Product D below.

• Product A when treated with NaSCH2CH3 gives Product B (optical rotation ?D = +25°).

• Optically pure (R)-(-)-2-butanol when treated with PBr3 gives Product C (?D = +38°).

• Product C when treated with NaSCH2CH3 gives Product D (optical rotation of ?D = -25°)

(c) (2pts) What is the absolute configuration of Product B? ________________

(d) (2pts) What type of mechanism is involved in the formation of Product C? ________________

(e) (4pts) Propose an arrow-pushing mechanism to clearly illustrate the mechanistic step indicated in part

(d) that is also consistent with the stereochemical information provided. You do not need to show the entire mechanism. Just show the step that is relevant to setting the stereochemistry observed in the product.

2. Consider the two reactions below.

(a) (4pts) Briefly explain why one of the reactions above will produce a single product while the other will produce a mixture of two stereoisomers.

(b) (6pts) To the right of each reaction arrow in the scheme above, draw the expected alky halide product(s) for each reaction.

(c) (4pts) For the case that produces a mixture of stereoisomers, indicate (i) what type of stereoisomers are produced and if (ii)they are produced as a racemic mixture. Write your answer in the space below.

(i) ____________________________________ (ii) _____________________________________

3. (18pts) Where products are missing, draw the structure of the major organic product expected. Where a product is shown, draw the structure of the missing starting substrate necessary to complete each transformation. In all cases, show stereochemistry clearly where applicable.

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