On the Proton Shuttle Motion in Protonated Acetylene: An Electronic Structure Perspective

The Grothus like hydrogen motion in the inter-conversion of classical to non-classical conformation of protonated acetylene is studied in the purview of the electronic structure perspective. The reorganization of electrons during the proton transfer is explored by means of the changes in structural features, partial charges, natural bond orbital and normal mode analysis following an intrinsic reaction coordinate (IRC) connecting classical and non-classical structures. It is found that conversion of classical to non-classical structures along the IRC occurs due to the charge donation to the vacant non-bondingp-orbital of asphybridized carbon from the adjacent C-H sigma-bond which facilitates the delocalization of electron and leads to gain in stabilization energy. This interaction continues till post transition state, gradually weakens and is finally decomposed to two non-bonding orbitals, onep-orbital onsp(2)carbon and ones-orbital on migrating hydrogen. From this point, the migrating hydrogen in turn accepts and donates electrons simultaneously from thep-orbital onsp(2)carbon and non-bondingp-orbital ofsphybridized carbon, respectively, to finally arrive at the non-classical structure.