Water-Assisted Isomerization from Linear Propargylium (H2CCCH+) to Cyclopropenylium (c-C3H3+)

Calculations at the QCISD(T)/6-311+G(d,p)//B3LYP/6-31G(d) level indicate that the participation of water can effectively lower the isomerization barrier from linear propargylium (H 2 CCCH + ) to cyclopropenylium ( c -C 3 H 3 + ). With the increase of the amount of H 2 O ( n H 2 O, n = 1, 2, or 3) participating in the isomerization, the isomerization barrier decreases, and with three H 2 O molecules the isomerization becomes nearly barrierless. In contrast to previous studies on the catalytic effects of water on carbonyl systems and the reaction of H 2 O(g) with SO 3 (g), the so-called reactant and the catalyst do not associate into cyclic structures, but rather into open-chain structures. This work may be useful for further studies on the catalytic effect of other species having lone electronic pairs, such as H 2 S, NH 3, and HF.