Protonation of Pyrrole and Furan by H3O+ and NH4+ in the Gas Phase: A Density Functional Theory Study

Abstract

Density functional theory and ab initio calculations have been used to determine structures and stabilities of the protonated aromatics species AH+ and AH22+ (A=pyrrole, furan). Possible mechanisms and relative energetics for protonation of pyrrole and furan by H3O+ and AH4+ in the gas phase have been explored. Calculations show that the Cα-protonated species was the most stable structure for AH+, and the protonated AH+ might accommodate the second proton to yield AH22+ if the free proton was available. The gas-phase H3O+ could protonate pyrrole and furan with significant exothermicity and almost without barrier. The proton transfer from AH4+ to pyrrole and furan has a barrier ranging from 33.5 to 39.3 kJ/mol in the gas phase.