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#1 Posted : Monday, August 09, 2021 7:28:28 PM
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2) I understand that with a thermodynamic mixture, the greater amount produced the more stable it is, but for a kinetic mixture, would it be correct to say that 4a is the more favourable kinetically?

3) Does a dehydration reaction lead to the formation of a double bond?

9) I had a question regarding the answer explanation for this one. It mentions that more stable compounds have a lower enthalpy of combustion, I thought more stability meant that more heat was given off? Also, would this be true for enthalpy of formation as well?

35) I understand that HRP causes oxidation of phenols, but why is a ketone not formed as it is a secondary alcohol? Also, why can it not be option B as HRP can also cause oxidation of amine?

37) For this question, I thought nitrogen would be a better Lewis base than oxygen as it is less EN and would be able to donate its electrons more easily? Also, how does nitrogen have a partial positive charge?
#2 Posted : Friday, August 13, 2021 4:25:37 PM
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Hi Moiz!

Q2: A thermodynamic mixture will favour the more stable product, as you've said. A kinetic mixture will favour the faster-forming product.

I'm not certain how this would change if the kinetic product were favoured. I think they would have to give this information in the passage, similar to how they've given you the breakdown of 60:40 in this passage, and then asked you to explain WHY 4a is more favoured than 4b based on the information given. I think they've set up the experiment to favour the thermodynamically-favourable product, and they are simply asking you to observe that. At low temperatures, the kinetic product would be favoured, but that would have to be determined experimentally.

Q3: Yes!

Q9: Let's consider two examples: diesel and biodiesel. Biodiesel is made by transesterifying plant oils.

A substance with a HIGH heat of combustion has a lot of energy to give away when it burns, and is therefore a good fuel. A substance with a LOW heat of combustion does not have a lot of energy to give away when it burns, not as a good of a fuel.

The heat of combustion of diesel is 42 MJ/kg.
The heat of combustion of biodiesel is 37 MJ/kg.

Diesel releases more energy, and is therefore a better fuel than biodiesel. Aww nuts. So, biodiesel is more stable, but that's not good for us if we want to replace diesel with biodiesel on an environmental level.

Yes, the same is true for enthalpy of formation.

Q35: Peroxides form radicals (single electron species). Answers A, B, C, and D are all radicals, so that doesn't really help us. The key is the catalyst, HRP, will dictate what KIND of radical forms. In the passage, it says that HRP "catalyzes the oxidation of AROMATIC amines and phenols". So, the peroxide will ONLY target an amine that is CONNECTED TO an aromatic ring or a hydroxyl group CONNECTED TO an aromatic ring (e.g., phenol group). Thus, A is the best answer.

Q37: You've got it narrowed down to a really good 50:50 -- between N and O. Great!

OK... to decide between N and O, let's look back at the passage.

They mention "calcium ions are coordinated by various Asp, Ser, Thr, Gly, and Ile residues through both side chain and backbone interactions".

Let's take serine as an example: https://file.medchemexpr...roduct_pic/hy-n0650.gif

Through the magic of RESONANCE (aww nuts), we can see that oxygen acts as a better Lewis base than nitrogen:


because oxygen has a partially NEGATIVE charge, while nitrogen has a partially POSITIVE charge.

Therefore, D is the best answer to this question.
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