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AAMC FL#4
Moiz_6047
#1 Posted : Thursday, August 12, 2021 2:15:31 AM
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Q30: I know that an ester can be reduced to form a primary alcohol, but can a primary alcohol be oxidized to form an ester?

Q31) Would really appreciate some guidance on this one. A little lost on how to approach it!

32) How do we know this is Sn2 and not Sn1 as the reaction is very bulky.

41) I understand why C,D can be eliminated, but can you please explain why A is a better answer than B?
INSTR_Katrina_128
#2 Posted : Friday, August 13, 2021 4:57:44 PM
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Hi Moiz!

Q30: Not directly, from my understanding. You first need to oxidize the primary to a carboxylic acid using a very strong oxidizer (like potassium dichromate). Then, the carboxylic acid can be esterified with alcohol to form an ester under acid catalyst.

I'm sure there are more complex mechanisms, but these mechanisms are for organic chemists to research! 😀

Q31: This one's really really tough! First, you need to block out everything in the passage except for Compounds 3 and 4.

Next, I think this image will help you a lot! 😀 It is the full mechanism drawn out.

https://i.imgur.com/xODRFuT.jpeg

Q32: A secondary carbon atom would favour SN2. Only tertiary would favour SN1.

Q41: Great job getting rid of C and D. Now to figure out if it's A or B...

Very tricky, but it comes down to this: we are told that Asp14 is the nucleophile, so it will attack the substrate. Which atom on Asp14 SPECIFICALLY will be the nucleophile? The side chain of Asp has a carboxyl group, so an OXYGEN atom will be the nucleophile! An oxygen will not attack another oxygen... that doesn't make any sense chemically. We don't see O-O bonds very often (unless there is an ether being formed). Therefore, the nucleophilic attack will occur FROM the oxygen group on Asp14 TO the phosphate group of the substrate.

Therefore, A is the best answer.
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