At -40 degrees C = 1, 2-addition across a conjugated diene (kinetic control)
At higher temperatures = 1,4-addition (thermodynamic control)
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1 2 3 4 (sorry for the crappy picture, but let's say that's a double bond, single, and then a double.
If I had H-Cl in -40 degrees C, the H would be added to carbon 1 leaving a carbocation at carbon 2. Cl adds on to carbon 2.
