Experiment 2 - R-(-)-Carvone,dihydroxylation, electrophlic addition. Final versino

Experiment 2 - R-(-)-Carvone,dihydroxylation, electrophlic addition. Final versino

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Experiment 2 A. Regioselective epoxidation of R-(-)-carvone with MCPBA B. Syn dihydroxlation of alkenes with KMnO 4 on a TLC plate C. Electrophilic addition of bromine with cholesterol Lut Ming Cheng, 4957880, CHM2123, Section C Talal Zafar, 4827101, CHM2123, Section C TA: Wendy Campbell Due Date: October 6, 2008 1 – Theory and Mechanism Epoxidation reactions are regioselective. As the rate of the reaction is depended on the electron density of the double bond, the reaction would favour the double bond that is more electron-rich than the other. In addition, the more electron-rich double bond would react faster. In the experiment, (R)-(-)-carvone undergoes the epoxidation reaction with MCPBA. (R)-(-)- carvone has two carbon-carbon double bonds. The epoxidation would favour the carbon-carbon double bond on the isopropenyl group, because it is much richer electron than the one that is adjacent to the carbonyl group. The regioselective epoxidation of (R)-(-)-carvone with MCPBA is shown in below, CH 3 O C H 2 CH 3 MCPBA CH 2 Cl 2 Na 2 SO 3 1. 2. CH 3 O CH 3 O The epoxidation reaction is then followed by TLC analysis. The TLC analysis is aimed to verify the completion and the product of the reaction. Furthermore, potassium permanganate is then added to the TLC plate to detect the existence of double bond in the final product. Potassium permanganate reacts with the double bond and makes the spot yellow-brown. The potassium permanganate reaction is shown as follows, CH 3 O CH 3 O KMnO 4 H 2 O 1. 2. CH 3 O CH 3 O O H O H H K + MnO 2 + Electrophilic addition is an exothermic reaction, in which a pi bond is turned into a sigma bond. The double bond in the alkene acts as a nucleophile. Halogens, halogen acids, hypohalouse acids, sulphuric acid and water can be used as the electrophlic reagent. In this experiment, bromination of cholesterol is performed. The electrophlic attack of Br 2 generates a cyclic bromonium ion. The addition gives a trans stereochemistry to the bromonium ion. As the Br - attacks the most substituted carbon in anti-periplanar fashion by S N2 reaction, it would result in the inversion of configuration at that specific carbon. Furthermore, bromine can act as a qualitative test to identify the existence of bonds in the reaction. If the bromine reacts in
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electrophilic addition, the red colour of bromine would disappear from the solution. It also means that alkene was present. The electrophlic addition mechanism of bromine with cholesterol is shown as follows, C H 3 CH 3 CH 3 O H CH 3 CH 3 Br 2 C H 3 CH 3 CH 3 O H CH 3 CH 3 Br Br 2- Table of reagents and solvents A. Regioselective epoxidation of (R)-(-)-carvone with MCPBA Compound Molar Mass (g/mol) Amount Density (g/mL) mmol equiv. MCPBA
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This note was uploaded on 11/13/2010 for the course CHM CHM2132 taught by Professor Goto during the Fall '07 term at University of Ottawa.

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Experiment 2 - R-(-)-Carvone,dihydroxylation, electrophlic addition. Final versino

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