Selenophenes protophilic

Protophilic exchange of deuterium proceeds 50,000 times faster at an a than at a /3 position of selenophene. An electron-donating methyl group hinders the exchange, and this effect is most pronounced in 2-deuterio-3 - me thylselenophene. 

Isotope exchange is a technique which gives reliable comparative data on the electrophilic and protophilic reactivity of the five-membered heterocycles furan, thiophene, and selenophene, revealing how the activity of their hydrogen atoms varies with the position of the hydrogen in the ring and with the number and position of substituents. The results from kinetic data on isotopic exchange in deuterated selenophenes, thiophenes, and furans, may be summarized as follows. 

The protophilic exchange rate for a-deuterium atoms differs from that for ft atoms by a factor of 50,000 in selenophene, 250,000 in thiophene, and 500 in furan. 

The structures below summarize hydrogen activities of selenophene, thiophene, and furan in protophilic isotope exchange the rate constant of deuterium exchange at the a position of furan is arbitrarily given the value of unity. 

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See also in sourсe #XX -- [ , ]

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