Does 4-Iodoniacyclopentene Exist?

摘要

The addition of electrophilic iodine to the most stable s-trans-butadiene may occur with the initial formation of 4. Direct nucleophilic attack on 4 would give the 1,2-product, while the 1,4-product with trans configuration could be formed by attack at the 4 position (S_N2′-type mechanism), favored by π conjugation from the vinyl group. The barriers for the interconversion between 4 and 3 (through 5) are high and, thus, equilibration to the more stable 4-iodoniacyclopentene (3) is prevented and the 1,4-products with cis configuration have not been observed experimentally. However, because 3 is the global minimum, the existence of 4-iodoniacyclopentene still remains open. These results should encourage experimentalists to search for this species by an alternative method. In this sense, Table 2 shows the calculated vi-brational frequencies (scaled by 0.94) and IR intensities for 3.