kinetic vs thermodynamic control of a reaction

[inaccensa]

can anyone please explain the difference between the 2.

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[loveoforganic]

Kinetic product is the product that forms faster (lower activation energy). It is often the less stable final product, but not always (i.e. it is possible for a kinetic product to also be a thermodynamic product). When there are different kinetic and thermodynamic products, the reaction is carried out at the minimum temperature possible, so that less molecules have the energy to make it over the higher activation energy associated with the thermodynamic product.

The thermodynamic product is the most stable final product (most negative change in gibbs free energy). This product is often associated with a higher activation energy, but that is not always the case (it can be the kinetic product too).

An example of a kinetic/thermodynamic competition is addition across a conjugated diene, where you often have the potential to either arrive at the 1,2-disubstituted product (kinetic, because there's a more stable carbocation intermediate and thus a lower activation energy, but not thermodynamic, because your alkene is generally less substituted) or the 1,4-disubstituted product (thermodynamic, because the final product generally has the more substituted alkene).

 

[sv3]

Kinetic product is the product that forms faster (lower activation energy). It is often the less stable final product, but not always (i.e. it is possible for a kinetic product to also be a thermodynamic product). When there are different kinetic and thermodynamic products, the reaction is carried out at the minimum temperature possible, so that less molecules have the energy to make it over the higher activation energy associated with the thermodynamic product.

The thermodynamic product is the most stable final product (most negative change in gibbs free energy). This product is often associated with a higher activation energy, but that is not always the case (it can be the kinetic product too).

An example of a kinetic/thermodynamic competition is addition across a conjugated diene, where you often have the potential to either arrive at the 1,2-disubstituted product (kinetic, because there's a more stable carbocation intermediate and thus a lower activation energy, but not thermodynamic, because your alkene is generally less substituted) or the 1,4-disubstituted product (thermodynamic, because the final product generally has the more substituted alkene).

wow i never encountered this stuff before.......nice answer

 

[austinap]

Kinetic product is the product that forms faster (lower activation energy). It is often the less stable final product, but not always (i.e. it is possible for a kinetic product to also be a thermodynamic product). When there are different kinetic and thermodynamic products, the reaction is carried out at the minimum temperature possible, so that less molecules have the energy to make it over the higher activation energy associated with the thermodynamic product.

The thermodynamic product is the most stable final product (most negative change in gibbs free energy). This product is often associated with a higher activation energy, but that is not always the case (it can be the kinetic product too).

An example of a kinetic/thermodynamic competition is addition across a conjugated diene, where you often have the potential to either arrive at the 1,2-disubstituted product (kinetic, because there's a more stable carbocation intermediate and thus a lower activation energy, but not thermodynamic, because your alkene is generally less substituted) or the 1,4-disubstituted product (thermodynamic, because the final product generally has the more substituted alkene).

The temperature the reaction is run at depends on which product is desired. If there is a difference between the two products, higher temperature favors the thermodynamic product while lower temperature favors the kinetic product.

There are are implications as far as which reagents to use. E.g, if you want to make an enol, really strong bases favor the kinetic product, whereas weaker bases favor the thermodynamic product (assuming they are different).

In the above image, there are two reactions, from R --> A and R --> B. In this case, A is the thermodynamic product since it is lower in energy than product B, and is thus more thermodynamically stable. B is the kinetic product, since there is a lower activation energy to reach this product than product A.

 

[loveoforganic]

Your link isn't working still, but enolates are another good example. Do you know if sterics tie into the kinetic/thermodynamic competition or if it's simply the inductive effect of added alkyl groups destabilizing the thermodynamic intermediate?

sv3 - Thanks, I'm sure you've encountered it and just forgotten it though Pretty sure that stuff is broadly taught in organic.

 

[inaccensa]

thanks a lot