1,2 addition and 1,4 addition

[atlanta213]

AT low temp, conjugate diene - 1,2 addition.
At high temp, conjugate diene- 1,4 addition.

I know those two facts but can not apply.

Could you guys explain this?

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[Maygyver]

AT low temp, conjugate diene - 1,2 addition.
At high temp, conjugate diene- 1,4 addition.

I know those two facts but can not apply.

Could you guys explain this?

This occurs with a conjugated carbonyl compound. In 1, 4 addition the Nu will attack the carbon before the double bond and the double bond will push the electrons from the double bond of the oxygen onto the oxygen to give it a negative charge. The oxygen will then get protonated. In a 1,2 addition, the Nu will attack the carbonyl carbon and the oxygen will get protonated again. I don't know how to draw out the compounds but I hope this helps.

 

[Thundercatz]

Ill try my best....

Lets say you have 1,3 butadiene which will react with with HCL.

For a 1,2 reaction, lets say the double bond at the 3rd position will attack the hydrogen on the HCL leaving a positive charge at the 3rd position on the diene. The CL, now a nucleophile, will then attack the positive charge. This is 1,2 addn since the the CL and H are added next to each other.

For 1,3, the double at the 3rd will still attack the hydrogen on the HCL and leave the a positive charge at the 3rd carbon. Now the double at the 1 position will shift over, and leave a positive charge at the one position on the diene. The CL will now attach that positive charge. The CL is now at the one position and the H at the 4. This is 1,4 addn.

I hope this helps and doesnt confuse you more LOL.

 

[atlanta213]

I got it now. Thanks buds

 

[IDoWhatIWant]

This occurs with a conjugated carbonyl compound. In 1, 4 addition the Nu will attack the carbon before the double bond and the double bond will push the electrons from the double bond of the oxygen onto the oxygen to give it a negative charge. The oxygen will then get protonated. In a 1,2 addition, the Nu will attack the carbonyl carbon and the oxygen will get protonated again. I don't know how to draw out the compounds but I hope this helps.

1,2 and 1,4 also applies to carbonyl carbons? I thought only dienes. Oy, I'm so lost.

 

[drgreen]

Looking at the diagram, the 1,2-addition uses the more stable transition state (resonance form) while the 1,4-addition forms the more stable product.

more stable product=thermodynamic (the heat/energy is available to overcome the less favorable transition state, namely the primary carbocation).

more stable transition state=kinetic product (faster reaction occurs because the rate determining step is the transition state)

 

[DRHOYA]

Looking at the diagram, the 1,2-addition uses the more stable transition state (resonance form) while the 1,4-addition forms the more stable product.

more stable product=thermodynamic (the heat/energy is available to overcome the less favorable transition state, namely the primary carbocation).

more stable transition state=kinetic product (faster reaction occurs because the rate determining step is the transition state)

Thanks man!👍

 

[Maygyver]

Misread question.

 

[Maygyver]

1,2 and 1,4 also applies to carbonyl carbons? I thought only dienes. Oy, I'm so lost.

Uh yes...did you skip that chapter? lol. I'll go get my notes in a few.