Quiz6cor_E - changes overall(2 points Look for the...

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CHM 2123, Quiz #6: Oxidation and Reduction MARKING SCHEME Posted: October 22, 2009 Due: October 26, 2009 before 5pm 1. Rank the following electrophiles from the most to the least reactive in the presence of NaBH 4 . VERY Briefly justify your answer, with the use of keywords. (3 points) Note: Be careful, the order of compounds is different than on the actual quiz. Ph O Ph O Ph Me O Ph H O Ph OMe O ~ > >> similar reactivity: H gives less electrons than C but the adjacent carbonyl activates the "ketone" NaBH 4 does not reduce esters we can draw a resonance structure in which the OMe lone pair donates its electron density to the C=O, making it less electrophilic (E+) • Me gives more electrons than H: C=O less E + • more hindered than RCHO 2. How would you monitor the oxidation of p-nitrobenzylalcohol to p- nitrobenzaldehyde by IR spectroscopy? Hint: you’re looking for two major
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Unformatted text preview: changes overall. (2 points) Look for the disappearance of a large (broad) peak at 3200-3650 cm-1 (O-H stretch), and the appearance of a large peak at ~1700 cm-1 (carbonyl stretch of the aldehyde). 3. Why can’t tert-butanol be oxidized by sodium dichromate under the same conditions you will be using for your oxidation? Illustrate with a mechanism. (3 points) Tertiary alcohols don’t have the beta proton necessary for the oxidation step: 4. Following the oxidation reaction, why do you wash the ether phase with 1M NaOH? (2 points) . This deprotonates the carboxylic acid to the water-soluble salt, and so it can be separated from the aldehyde which stays in the ether phase (purification)....
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This note was uploaded on 01/13/2010 for the course CHM chm2526 taught by Professor Louise during the Spring '09 term at University of Ottawa.

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Quiz6cor_E - changes overall(2 points Look for the...

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