1,4-Addition vs. 1,2-Addition (ochem confusion)

[123321]

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Can someone please explain the difference? For example, why does HBr, 50 deg C add 1,4 and HBr -20 deg C adds 1,2?

I keep coming across these problems and have tried to brush them off, but now they're really getting to me 🙁

#Help.

 

[DAT Destroyer]

1,2 addition goes through a kinetic control. At low temperature molecule goes to the most stable carbocation, which forms the fastest.