The reactions and properties of a series of chalcogen-containing compounds (CH(3))(2)X, and (CH(3))(2)C=X, where X = O, S, and Se, were studied computationally at the CBS-QB3 level to examine the differences among these molecules. The reactions and properties investigated include the double bond dissociation energy, the ionization potential, the interaction energies with a series of acids including a proton, CH(3)(+), Li(+), MeLi, and MeOH, and the enolization energies of the (CH(3))(2)C=X species. The effect of substituting the O of acetamide with S or Se also was studied. The changes that result from these reactions were examined via changes in structure and changes in charge distribution using the Hirshfeld charges.