HT3an-03 - C hemistry 301-301A Answers to Hour...

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Chemistry 301-301A - Answers to Hour Examination #3 1a. Standard hydration with rearrangement, and right off the last hour exam as well. Protonation goes to give the secondary, not primary carbocation, and a hydride shift then generates the more stable tertiary carbocation. 1 OH OH + H 2 O H 3 O + 2 3 O + H 2 O H H H 2 O H 3 O + H 2 O O H H H 2 O hydride shift b. In the transition state for hydroboration, boron is δ and carbon is δ + . Therefore the boron becomes attached to the less substituted end of the double bond, thus “locking in” the observed regiochemistry. There is never an opportunity for rearrangement. RBH 2 R 3 B BH 2 BH 2 H OH 1 1. BH 3 2. HOOH/HO 4 δ δ transition state = repeat two times 3
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c. Addition of BH 3 is reversible at high temperature, as the question says. Thus, at 160 °C the initial borane can either revert to starting material or go on to a new alkene, X = 1 , that can hydroborate anew: 5 2. HOOH/HO OH 4 BH 2 1. BH 3 X = 1 BH 3
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2. At first sight, it might seem that all of the chemistry of 1a would be repeated. After all,
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This note was uploaded on 03/07/2010 for the course ORGO 1 AND V.0243 taught by Professor Jones during the Spring '10 term at NYU.

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HT3an-03 - C hemistry 301-301A Answers to Hour...

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