1,2-addition proceeds faster than 1,4 addition making excess of 1,2-adduct at low temperatures. Also, since conversion of 1,2-adduct to 1,4-adduct is faster than the reverse, 1,4-adduct is in excess at high temperatures. Both facts account for the same thing, that activation energy for 1,2-addition less than that for 1,4-addition to conjugated dienes. But why?
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I'm not sure if it's an outright duplicate, but I covered this topic in a previous question: Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control – orthocresol Feb 19 '18 at 02:41