Browsing by Author "Afriyie, Bright Aryeh"

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    Trapping of 1,2-cyclohexadiene: A DFT mechanistic study on thereaction of 1,2-cyclohexadiene with olefins and nitrones
    (Elsevier Inc, 2018-02-13) Boafo, Emmanuel Amoah; Darko, Kwabena; Afriyie, Bright Aryeh; Tia, Richard; Adei, Evans
    The mechanistic aspects of cycloaddition reactions of 1,2-cyclohexadiene with olefins and nitrones havebeen investigated with DFT calculations. The results show that the cycloaddition reactions of 1,2-cyclohexadiene with olefins do not go through a concerted pathway (one-step mechanism) but rathera stepwise one involving the formation of a biradical intermediate which then closes to formfinalcycloadduct. Electron-withdrawing substituents on the 1,2-cyclohexadiene decrease the activation bar-rier of the biradical-forming step but increase the barrier of the product-forming step and productstability, while electron-donating substituents on the 1,2-cyclohexadiene increase the barriers for boththe biradical-forming step and the product-forming step but decrease the product stability. In the re-action of 1,2-cyclohexadiene with nitrones, the four pathways investigated have activation barrierswithin 1 kcal/mol of one another, the lowest being 10.45 kcal/mol and the highest 11.04 kcal/mol,indicating that these reactions are very unselective. Electron-withdrawing groups on the nitrone increasethe stability of the resulting products whereas electron-donating group on the nitrone decrease thestability of the resulting products. The [3þ2] cycloadduct proceeds to the formation of a more stableformal [5þ2] cycloadduct if a phenyl substituent is present on the nitrogen of the nitrone.