Previous research has shown that the regioselectivity of a halogen under kinetic conditions in an electrophilic addition reaction with a conjugated diene is driven by the localization of the positive charge on carbon-2 of the conjugated pi system of an alkene. In addition, the previous research indicates that the proximity effect, or simply the effect of the nucleophilic halogen being closer to the carbon-2, influences the dominance of the 1,2-adduct over the 1,4-adduct under kinetic conditions. It is unclear whether the dominance of the formation of the 1,2-adduct under kinetic conditions is driven by the charge effect, the proximity effect, or a combination of both effects. To determine what is driving the formation of the dominant 1,2-adduct, a synthesis procedure was conducted using 2,5-dimethyl-2,4-hexadiene as our conjugated diene and HBr dissolved in acetic acid as our nucleophile under kinetic conditions. Due to the carbocation formed after the electrophilic attack of the hydrogen of HBr, if the proximity effect is more influential than the charge effect, the dominance of the 1,2-adduct will result in greater formation of 2-bromo-2,5-dimethyl-4-hexene than 4-bromo-2,5-dimethyl-3-hexene. Further if the charge effect is more influential than the proximity effect the dominance of the 1,2-adduct will result in a greater formation of 4-bromo-2,5-dimethyl-3-hexene than 2-bromo-2,5-dimehtyl-4-hexene. Lastly if both the charge effect and the proximity effect influence the formation of the 1,2-adduct equally under kinetic conditions than there should be a 1:1 ratio of 2-bromo-2,5-dimethyl-4-hexene and 4-bromo-2,5-dimethyl-3-hexene. The resulting products were analyzed using IR spectroscopy, GC/MS, <sup>1</sup>H NMR, and <sup>13</sup>C NMR.

Proximity vs. charge effect determining the ratio of 1,2-adduct vs. 1,4-adduct under kinetic conditions using 2,5-dimethyl-2,4-hexadiene

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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