For many years, a controversy raged concerning the structures of so-called “electron-def...

For many years, a controversy raged concerning the structures of so-called “electron-deficient” molecules, that is, molecules with insufficient electrons to make normal two-atom, two-electron bonds. Typical is ethyl cation, C₂H₅⁺ , formed from protonation of ethene.

Is it best represented as an open Lewis structure with a full positive charge on one of the carbons, or as a hydrogenbridged structure in which the charge is dispersed onto several atoms? Build both open and hydrogen-bridged structures for ethyl cation. Optimize the geometry of each using the B3LYP/6-31G* model and calculate vibrational frequencies. Which structure is lower in energy, the open or hydrogenbridged structure? Is the higher energy structure an energy minimum? Explain your answer.