SB C/P #20

[salemstein]

If I understood the question correctly, compound 1 didnt react when mixed, while compound 2 did. Wouldnt that mean C1 is under thermodynamic control instead b/c mixing didnt overcome the Ea? Looking at C2 though, mixing cause new liposome to form, so wouldnt that be a kinetic product b/c it more easily overcame Ea?

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[theonlytycrane]

post the question

 

[salemstein]

Oops here:

 

[Astra]

Oops here: View attachment 202293

C1 was able to mix.

C2 caused formation of a new product which was the expected final concentration.


The expected final concentration indicates that once this is reached, the product is most stable. So this means thermodynamic control.

C1 was able to mix, so this means the Ea was overcome. Nothing about product stability or concentration is mentioned, so I eliminated thermodynamic control.

So, that leaves C1 as kinetic and C2 as thermodynamic control

 

[aldol16]

This question didn't quite logic out to me either. Kinetic control refers to the product expected if only kinetics are taken into account - that is, which reaction is the fastest. Thermodynamic control refers to the product expected if enough energy is present so that the global minimum is reached. It seems that Compound 1 is the thermodynamic product and compound 2 is the kinetic product since upon mixing, compound 2 goes to a more stable form.

 

[NextStepTutor_2]

This question has been debated elsewhere. It is not the best of questions from the AAMC. They do make missteps, more so in the past year with this new exam as they adjust to their new exam. I follow their "logic" for compound 2, but not so much for compound 1

Passage info on mixing experiment:

"The researchers mixed liposomes of different sizes and observed that those formed from Compound 1 were stable to mixing, but mixing those from Compound 2 formed new liposomes with an average size expected for the effective final lipid concentration."

Justification in their "explanation"

I think what they are trying to get at it is that mixing (adding E to the system, causing them to interact with each other and potentially rearrange?) did nothing to effect the liposomes from C1, indicating a lack of thermodynamic controls in favor of kinetic control. The mixing of C2 liposomes led to rearrangement to new, intermediate-sized molecules, indicating an adjustment to a new stability via a form of thermodynamic control.

 

[lostnconfused]

This question's also tripping me up.. Is there a difference between thermo/kinetic product vs. control?

 

[aldol16]

This question's also tripping me up.. Is there a difference between thermo/kinetic product vs. control?

Not really - the kinetic product is usually the product that kinetic control leads to, although you could use control in a difference sense. Chemically, one could use control to refer to any manipulation that alters the outcome of a reaction such that it achieves your desired end. So for example, let's go back to a simple organic chemistry example - forming an enolate. There's a thermodynamic enolate (more substituted -ene) and the kinetic enolate (less substituted -ene). The kinetic enolate is the kinetic one because it's the least sterically hindered and thus faces the lowest kinetic barrier to formation. Now if you do this at room temp, there will be enough thermal energy around to cause formation of the thermodynamic product. In other words, the system will settle into the thermodynamic state. But now if you do it at -78 degrees Celsius, you can obtain only the kinetic product. So the kinetic product - the less substituted enolate - is the outcome of kinetic control.

 

[lostnconfused]

Not really - the kinetic product is usually the product that kinetic control leads to, although you could use control in a difference sense. Chemically, one could use control to refer to any manipulation that alters the outcome of a reaction such that it achieves your desired end. So for example, let's go back to a simple organic chemistry example - forming an enolate. There's a thermodynamic enolate (more substituted -ene) and the kinetic enolate (less substituted -ene). The kinetic enolate is the kinetic one because it's the least sterically hindered and thus faces the lowest kinetic barrier to formation. Now if you do this at room temp, there will be enough thermal energy around to cause formation of the thermodynamic product. In other words, the system will settle into the thermodynamic state. But now if you do it at -78 degrees Celsius, you can obtain only the kinetic product. So the kinetic product - the less substituted enolate - is the outcome of kinetic control.

Yeah.. Hmm.. Idk then.. I'm totally with you on thinking that choice B had to be the right answer.