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problem set 5 key - orgo

problem set 5 key - orgo - WHY this reversal in...

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Monday Night Problem Set 5 Chemistry 221 1. Draw the structure of (3E, 5Z)-2,6-dimethyl-1,3,5,7-octatetraene. 2. Draw the major product for each of the following reactions. + HI a) b) + HBr Br I 3. Show the alkene(s) you could start with to make the following alkyl halides: Cl Cl best options This one is not a good choice. (It will give a mixture of addition products) Cl Even though HCl can add to this double bond in 2 ways, it doesn't matter -- you get the same product either way!
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4. Treating 1-methyl-1-vinyl-cyclopentane with HCl gives mainly the product shown. Propose an electron pushing mechanism for the formation of this product. + HCl Cl 1-methyl-1-vinyl-cyclopenane H Cl Cl Cl alkyl shift 5. Consider the following reaction: The observed products for this reaction are unusual in that they do NOT follow Markovnikov's rule. Write the mechanism for each of the two possible pathways for this reaction and use them to explain
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Unformatted text preview: WHY this reversal in regioselectivity is observed. Note – if you replace the benzene with a cyclohexane, only the usual Markovnikov addition product is observed. + H-Br As always, the H-Br can add two ways to this alkene. One would normally expect the reaction to proceed via the 3 o carbocation, but it turns out that this is not the favored pathway here. Despite being a 2 o carbocation, the first is a more stable carbocation, due to resonance delocalization of the positive charge throughout the benzene ring. The 3 o carbocation has no additional stability, so the top pathway turns out to be the energetically favored one. favored pathway + H-Br Br Major product Br Only trace amounts formed +...
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problem set 5 key - orgo - WHY this reversal in...

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