Why are more stable carbocations faster formed?

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In summary, the activation energy of a chemical reaction can depend on the thermodynamic stability of the formed carbocation as it plays a role in the stabilization of the transition state. This can affect the rate of the reverse reaction and ultimately impact the overall forward rate of the reaction. However, other factors such as steric hindrance also play a role in determining the rate.
  • #1
sludger13
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I have no idea how activation energy of a chemical reaction (in either direction) could depend on the thermodynamic stability of formed carbocation, as a product of that reaction. Activation energy of a chemical reaction should depend only on the structure of reagents, right?

The only thing I'm considering is that the more stable is a carbocation, the greater is the reaction enthalpy, thus it could (maybe) better heat the remaining reagents. And with greater Ek of that particles, then the reaction really run faster.
 
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  • #2
Or, the structure of (1°, 2°, 3°) carbon substitueted REAGENTS really prevent
from elimination of carbocation differently...
 
  • #3
Activation energy isn't the only factor. The extent to which a reaction occurs is the sum total of the forward and reverse reactions, which happen continuously. Most everything can and does reverse spontaneously to a certain extent, which is dependent on the stability of the reactants and the products.

In the case of carbocations, the molecule separates into its constituent ions. With enough activation energy, they can reverse and reform the full compound. Repeat ad nauseum. Steric hindrance makes the reversal of 3° more difficult than the reversal of 2° and 1°, but it still happens to a certain extent. These relative amounts of hindrance, and therefore the rate of the reverse reaction, are what determine the overall forward rate.

That's how I came to understand it in my organic classes, which were close to 4 years ago now, so somebody else may be able to explain it better or point out if I happened to get something wrong.
 
  • #4
Activation energy is the difference in energy between the reactands and the transition state. The factors stabilizing the Carbocation are also important in the stabilization of the transition state which resembles more the carbocation than the neutral reactands.
 
  • #5
DrDu said:
Activation energy is the difference in energy between the reactands and the transition state. The factors stabilizing the Carbocation are also important in the stabilization of the transition state which resembles more the carbocation than the neutral reactands.
This explanation seems fair to me, thanks.
 

1. Why are more stable carbocations faster formed?

More stable carbocations are formed faster because they have a lower energy state compared to less stable carbocations. This allows them to undergo reactions at a faster rate.

2. What factors affect the stability of a carbocation?

The stability of a carbocation is affected by the number of alkyl groups attached to the positively charged carbon atom, as well as the presence of any electron-withdrawing groups. The more alkyl groups and the fewer electron-withdrawing groups, the more stable the carbocation will be.

3. How does the stability of a carbocation affect its reactivity?

The stability of a carbocation greatly affects its reactivity. More stable carbocations are able to undergo reactions at a faster rate and with greater selectivity, while less stable carbocations may undergo undesired side reactions or may not even form at all.

4. Can the stability of a carbocation be predicted?

Yes, the stability of a carbocation can be predicted based on the number of alkyl groups and electron-withdrawing groups attached to the positively charged carbon atom. Generally, the more alkyl groups and fewer electron-withdrawing groups, the more stable the carbocation will be.

5. How does the stability of a carbocation affect the overall reaction mechanism?

The stability of a carbocation can greatly influence the overall reaction mechanism. More stable carbocations may undergo specific reactions, such as rearrangements, while less stable carbocations may only undergo simple addition reactions. The stability of a carbocation also affects the rate at which the reaction occurs and the overall yield of the desired product.

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