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Estudio teórico de la reacción hetero diels - alder [4+2] entre los sistemas N-(orto, meta y para nitrofenil)maleimida y (E)-1-isopropenil-2-fenildiazeno
...Orozco García, Luis Felipe | 2015-01-13
The presence of two nitrogen atoms more electronegative than carbon, combined with one or more substituent electro -atrayentes electron, origin in azo-alkene, especially 1,2-Diaza-1,3-dienes, a pronounced character electrophilic, and therefore their cycloadditions are predominantly inverse electronic demand (Lemos, Cycloaddition reactions of conjugated azoalkenes , 2010). However, the presence of neutral or more electron donating groups instead of the electro-attractive azo-alkene groups, and reaction with strongly electrodeficientes dienophiles, allow these dienes react via cycloaddition with normal electronic demand. Therefore, the present study evaluated through DFT methods, the mechanism for hetero Diels-Alder reaction with a normal electronic demand, among N-(o, m and p-nitrophenyl) maleimide systems and azo-alkene (E)-1-isopropenyl-2-phenyldiazene, B3LYP level theory / 6-311 + G (d). The results indicate that gas phase approach endo form, produces mechanisms kinetically favorable in all cases. Remarking a lower activation energy for the endo approach between m-nitrophenyl) maleimide and azoalkene. In all cases it is evident that such cycloadditions are exothermic. The formation of the cycloadducts takes place through a concerted asynchronous process, with the latest C-C bond formation (shorter link), compared to the formation of the C-N bond. From the values of charge transfer (CT) and overall electrophilicity difference (Δω), it follows that three cycloaddition may be classified as Diels - Alder nonpolar.
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