CHEM 205 Worksheet (WS7)

57 Points Total

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Key Topics: Alkene Addition Reactions

1. In the empty boxes (a-l), draw the structure of the MAJOR product expected following each alkene

addition reaction shown. Be careful, two of the reactions below will undergo a carbocation

rearrangement. (2pts for each product shown having correct connectivity of atoms)

Also include the following for the applicable:

• Show the relative stereochemistry of the product clearly using appropriate dashes/wedges for

each reaction letter indicated with ** (1pt each case for correct stereochemistry shown)

• Underline the two reaction products considered to be meso (2pts)

• Circle the only two reactions below that are Anti-Markovnikov alkene additions. (2pts each)

• For reaction (j) draw the major product in the favored chair conformation. (1pt)

2. The reaction shown below was performed as part of a research program funded by the National

Institute of Health (NIH) to develop therapeutic agents for the treatment of cocaine addiction.

(a) (15pts) Using what you have learned in Chapter 8 about the addition reactions of halogens with

alkenes draw a complete arrow-pushing mechanism for this process to include the following:

• Show all arrows for each mechanistic step, to illustrate correct electron flow

• Structures of all reaction intermediates formed in the mechanism must be shown correctly,

including the key cyclic iodonium ion intermediate

• Underline the iodonium ion intermediate that is formed in the reaction

• Stereochemistry of reaction intermediates consistent with the product stereochemistry shown

• Formal charges where applicable

(b) (2pts) Circle the correct option to describe the overall stereospecificity of this reaction.

Syn-addition or Anti-addition

(c) (3pts) Carbocation rearrangements are not possible in this reaction. This is due to the fact that a cyclic

halonium ion intermediate forms, rather than a more traditional carbocation intermediate. In one

sentence, explain why the cyclic halonium ion intermediate in general is considered more stable than a

carbocation, and in turn prevents any possible rearrangement from happening in this reaction?

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