[ORGO]conjugated diene

[ippie]

in an addition of conjugated diene, 1,2-addition occurs under kinetic control and 1,4-addition occurs under thermodynamic control.
I thought 1,2-addition occurs at room temperature, and 1,4-addition occurs at high temperature. Am I wrong?
then at 25 degree celcius, which occurs? I thought 1,2-addition, but Achiever test #2 (question #76) said 1,4-addition.
What is the border line of temperature of those two? 0 degree celcius?

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[blueclue]

1,2 is favored at 0 degrees and 1,4 is favored at 40.

 

[doc3232]

I just studied this...so -78 C is cold so bonds can't move around so the double bond stays at the 1 position and doesn't move, this is the way I think about it (I find this the easiest way to remember).
I think anything at room temp or higher will allow for the other product where the double bond becomes internal.
If the temperature is high enough then the other product is favored because there will be enough energy to have the double bond move to become internal. If the temperature is too low then the double bond will not move.
Hope I explained it well, I think I am right, Ochem book isn't around me right now.

 

[bruin432]

hey, just to be thorough.......1,2 addition is under kinetic control because of the two product opportunities it has the lower activation energy...in a situation where there are low temperatures (which are unfavorable towards the reaction) and a short time given for the reaction to progress....the 1,2 product will form because it takes less energy to create it. In warmer temperature, with a long time to react, the 1,4 product will form because while it may be higher in energy to achieve, it is the more stable alkene because it is more substitutes!! dont worry about exact temperature...just know lower temperatures will favor less activation energy which is the 1,2 addition prodcut, in this particular case. this is also possible with LDA and, which will form the kinetic enolate.