AAMC 8 Organic Questions

[huseyin]

hey:


I could not understand Q158-159 in AAMC 8. What is thermodynamic control and what is kinetic control of a reaction and how are they related to the experiment that has been presented? Well, I understand that kinetic control is dependent on activation energy, but why thermodynamically controlled reaction occurs at the eq?

oh, if some one can also explain #166 in AAMC 8, it would be great. I always freak out in these predominant conformation questions of cyclocompunds. Which compound goes axial, which one goes equilateral?

thanks everyone.

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[iwutitan]

Well... kinetic control means that whatever product forms faster is the major product while thermodynamic control says that whatever product is more stable is the major product. So if you have an equilibrium step then thermodynamic product is favored since no matter that the kinetic product forms faster, it can still go back due to the equilibrium, what is more important in this case is that the thermodynamic product is so stable that it doesn't want to go back to the starting material.
Furanadehyde's product in this case is more stable because it has the conjugate system that cyclohexanone doesn't have.
For question 166, it is easy if you draw the chair conformation of the ring. The more bulky group should be in the equatorial position.

 

[huseyin]

Well... kinetic control means that whatever product forms faster is the major product while thermodynamic control says that whatever product is more stable is the major product. So if you have an equilibrium step then thermodynamic product is favored since no matter that the kinetic product forms faster, it can still go back due to the equilibrium, what is more important in this case is that the thermodynamic product is so stable that it doesn't want to go back to the starting material.
Furanadehyde's product in this case is more stable because it has the conjugate system that cyclohexanone doesn't have.
For question 166, it is easy if you draw the chair conformation of the ring. The more bulky group should be in the equatorial position.

thanks man.