1,4 and 1,2 addition

[Ferdowsi]

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I don't understand the 1,4 and 1,2 addition. When do we use these? and What 's michael addition?...

 

[vhlam]

http://en.wikipedia.org/wiki/Michael_addition
i don't remember the specifics but 1,2 addition occurs when there is a strong nucleophile. 1,4 addition occurs when there is a weak, or as my ochem teacher liked to call it, "smooth" nucleophile.

 

[jjw822]

I don't understand the 1,4 and 1,2 addition. When do we use these? and What 's michael addition?...

i hope this will help you. Here it goes.

1,4 addition happens in thermodynamic control.

and 1,2 addition happens in kinetic control.

1,4 addition will give you more stable product but 1,2 addition will have more stable intermediate product which will lead to less stable product.

hope it helps

 

[Contach]

i hope this will help you. Here it goes.

1,4 addition happens in thermodynamic control.

and 1,2 addition happens in kinetic control.

1,4 addition will give you more stable product but 1,2 addition will have more stable intermediate product which will lead to less stable product.

hope it helps

and thermodynamic control is when the reaction is given heat
and kinetic control is when the reaction is in the cold.

you guys do a terrible job of explaining things.. i must say.. no one has mentioned the basic principle that michael addition occurs across a conjugated double bond system?

and I'm pretty sure vhlam is wrong? can som1 confirm?

 

[vhlam]

and thermodynamic control is when the reaction is given heat
and kinetic control is when the reaction is in the cold.

you guys do a terrible job of explaining things.. i must say.. no one has mentioned the basic principle that michael addition occurs across a conjugated double bond system?

and I'm pretty sure vhlam is wrong? can som1 confirm?

http://forums.studentdoctor.net/showthread.php?t=540418
kinetic and thermodynamic properties do apply, but you must also take into account the properties of the nucleophile. so i guess it's based on the problem.
btw, defining kinetic control as "when the reaction is in the cold," is pretty terrible.

 

[Contach]

congratulations. you have made me realize i dont even know what a 1,2 or 1,4 addition is.

can som1 explain how we will know if the reaction proceeds under thermodynamic or kinetic control?

thanks.

 

[jjw822]

congratulations. you have made me realize i dont even know what a 1,2 or 1,4 addition is.

can som1 explain how we will know if the reaction proceeds under thermodynamic or kinetic control?

thanks.

well.. what you said was right.

I remember a question that said reaction happened in -70 degrees which meant kinetic control.

I would say question will be pretty clear if it is thermo or kinetic by telling us the temp. like 200 degree will be thermo.

 

[211183]

Remember it in terms of the energy diagram...

Kinetic will prodeminate at low temp-- this will give you the FASTEST formed product ---- the less stable one with a lower activation energy (1,2)

forms faster because the transition state is more stable... not reversible


Thermodynamic will predominate at high temp--- this will give you the most STABLE product-- one with the highest activation energy (1,4) - this reaction will bein equilibrium

forms slower because the transition state is unstable--- but the product is much more stable than than the kinetic product



Kinetics is about speed --- get the product that forms faster because the transition state is more stable--- but you get a less stable product

Thermodynamics is about stabilities--- get product that forms slower because the transition state is less stable-- but the product is more stable (lower energy)


was that a bad explan?