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Tutor profile: Kelly K.

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Kelly K.
Microbiology University Student
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Questions

Subject: Organic Chemistry

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Question:

How do you get pinacolone from pinacol? List each step.

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Kelly K.
Answer:

Note: It is hard to do organic chemistry without visualizations. For any orgo question, I'd highly recommend drawing it out or using a model kit! First off, our starting reagent pinacol is a 1,2-diol with 4 methyl groups, 2 on each side. Our end product pinacolone is a ketone, which means it has two R groups on either side of the carbonyl. We can see we still have all of our carbons (we haven't lost any!), but we've lost an -OH group as well as a hydrogen on the second -OH of the diol, a net loss of: H2O! That second -OH can also be seen as "oxidized": the oxygen now is double-bonded to it's carbon. Now that we've seen what has happened, it'll be easier for us to use our mental "toolkit" of Orgo reactions to find the exact mechanism for this reaction. We know that we want to lose one of those alcohol groups, but we know that -OH isn't a very good leaving group because the -OH anion is a strong base and therefore very unstable in solution. So we'll want to make that alcohol into a good leaving group, and we can do that by protonating it to an oxonium with an acid. This oxonium is a good leaving group because it's conjugate base is... H2O! Once that oxonium leaves, we're left with a carbocation. We know that this positive charge prefers the most stable position possible: generally, stability of carbocations goes from tertiary>secondary>primary>methyl. How can we make this resultant carbocation more stable? We'll have to perform what is known as an alkyl shift: the "shift" of any alkyl group (methyl, ethyl, phenyl, etc.) to move a charge to a more stable adjacent place on the molecule. We have two methyl groups and an alcohol group on one side, and two methyl groups on the other where the positive charge is currently placed. That positive charge is going to move to the tertiary position on the other side, and it will do this by directing those electrons on the bond between one of those methyl groups on the alcohol side to the positive charge. Once the positive charge is below the alcohol, one of the oxygen's lone pairs is going to want to come down and stabilize that (remember, oxygen is a very electronegative atom!). This creates that double bond to the carbon that we want; however, that oxygen is still protonated! We'll want to deprotonate that: we can simply use a PT step (proton transfer) or, if you want to get into the dirty-details of it, H2O or the conjugate base from that acid we used to protonate pinacol in our first step will come and mop it up.

Subject: Writing

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Question:

What is wrong with the following sentence? "You can choose to study for a class in two ways, procrastinate until the last minute and stress or set a schedule, get tutoring help, and feel prepared.

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Kelly K.
Answer:

Semicolons! Many people don't realize how useful semicolons can be, or how to place them in a sentence. Semicolons generally separate two independent clauses (these are clauses that can be standalone sentences) that are related in topic, or can separate ideas/topics in a list that contains several commas. In this case, semicolons are exactly what we need to make this sentence more structured and easier to distinguish the two separate ideas we want to convey! "You can choose to study for a class in two ways: procrastinate until the last minute and stress; or set a schedule, get tutoring help, and feel prepared."

Subject: Biology

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Question:

What is the Red Queen Hypothesis in regards to why life evolves on earth?

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Kelly K.
Answer:

The Red Queen Hypothesis is a theory as to why biodiversity exists, as well as why organisms evolve and produce offspring with differing genes in the first place. It states that all organisms must evolve to stay ahead of the constantly-evolving pathogenic or competing organisms, as the original organisms would ultimately be out-competed if they did not. This provides an explanation as to why recombination occurs during gamete formation. It also provides an explanation as to why some extant species are asexual, as they do not have any parasites or competing organisms that would otherwise drive them to reproduce and diversify their gene pool.

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