The B3LYP density functional approach has been used to calculate the Cu+ binding energies of ethyl and vinyl amines, phosphines, and arsines. Geometries were fully optimized at the B3LYP/6-311G(d,p) level, and the final energies were obtained in B3LYP/6-311+G(2df,2p) single-point calculations. Significant differences between nitrogen-, phosphorus-, and arsenic-containing compounds have been found. For ethyl derivatives, the global minimum corresponds to the attachment of Cu+ to the heteroatom. However, whereas for P and As derivatives of agostic complexes in which the metal cation interacts with the hydrogen atoms of the XH2 or the CH2 groups are found to be stable, they are not for ethylamine. For vinylamine, attachment to C-beta is favored with respect to attachment to the heteroatom, whereas vinylphosphine and vinylarsine behave as P and As bases, respectively. The Cu+ basicity trends also differ from those found for the corresponding proton affinities. Thus, although ethylamine is more basic than ethylphosphine and ethylarsine when the reference acid is H+, ethylphosphine is the most basic compound when the reference acid is Cu+. For the vinyl derivatives, the Cu+ binding energies follow the trend P > As > N when only attachment to the heteroatom is considered, whereas the proton affinities follow the sequence N > P > As.