[AAMC 8] Thermodynamic v. stable product

[sc4s2cg]

This is BS Passage II, #102

Which semicarbazone is the product of thermodynamic control?

A) Cyclohexanone's, because the more stable product forms faster
B) Cyclohexanone's because it contains more alkyl substituents to a double bond than does the other product
C) 2-Furaldehyde's, because it is produced under equilibrium conditions and is more stable than the other product
D) 2-Furaldehyde's, because its potential energy is higher.

I am not sure if I am allowed to post the entire passage here, since it is crucial to answer the question. So I'll leave it off.

But the answer is C and it says because: "The melting point data in Table 1 indicate that the thermodynamically controlled product is the semicarbazone of 2-furaldehyde. The thermodynamically controlled product is the one that is formed under equilibrium conditions and is more stable."

But how can I tell which product was under equilibrium, or the most stable, from the passage? Experiment 2's products both had the same melting points, and Experiment 1's products had melting points that increased with temperature. They do not tell us what the products are.

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[rjosh33]

This is BS Passage II, #102

Which semicarbazone is the product of thermodynamic control?

A) Cyclohexanone's, because the more stable product forms faster
B) Cyclohexanone's because it contains more alkyl substituents to a double bond than does the other product
C) 2-Furaldehyde's, because it is produced under equilibrium conditions and is more stable than the other product
D) 2-Furaldehyde's, because its potential energy is higher.

I am not sure if I am allowed to post the entire passage here, since it is crucial to answer the question. So I'll leave it off.

But the answer is C and it says because: "The melting point data in Table 1 indicate that the thermodynamically controlled product is the semicarbazone of 2-furaldehyde. The thermodynamically controlled product is the one that is formed under equilibrium conditions and is more stable."

But how can I tell which product was under equilibrium, or the most stable, from the passage? Experiment 2's products both had the same melting points, and Experiment 1's products had melting points that increased with temperature. They do not tell us what the products are.

Generally you can tell how stable something is from its melting point data. The higher the melting point, the more stable it is (because it takes a greater input of energy to break the intermolecular forces). So, we notice that all of Exp 2's products melted at something like 200 deg C, because the reactants were mixed at 85 deg C. Exp 1 had increasing temps during its three runs, and the run with the highest temp. produced the product with the same melting point as those in Exp. 2.

Using that information, you can tell that the product formed from raised temps has to be the thermodynamic product. "Kinetic products" result from lower temps and form faster because of the lower activation energy of their reaction. However, thermo products have a higher activation energy, and so need a larger input of energy to overcome that barrier. They (thermo products) are also said to be more stable, and so have a higher melting point.