Organic Chemistry textbooks have long used the addition of HBr to 1,3-butadiene as a classic example of kinetic vs. thermodynamic control. At high temperatures the thermodynamically favorable 1,4-addition product predominates. At low temperatures, the less stable 1,2-addition product predominates. The traditional explanation for this is that the activation energy of the 1,2-addition is lower, thus its rate is faster. Some texts, citing a 1979 experiment by Eric Nordlander, are stating that the real reason is what is being called a proximity effect. We are currently charting and will report on the movement towards this explanation in textbooks. In an attempt to better our understanding of this reaction, we are currently studying the addition of HBr to simple alkene systems, such as hexene, and 2,5-dimethyl -2,4-hexadiene. The hexene substrate studies are being conducted to help maximize product yield for the addition of HBr across a double bond. Coupled with this effort, the 2,5-dimethyl -2,4-hexadiene substrate moves the greater charge to carbon 4, allowing us to see if that charge plays a significant role in the determination of product ratios.

Kinetic control mechanism: 1,2 vs. 1,4 addition in conjugated dienes

249th National Meeting (2015)

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