Inner-shell excitation spectra of gaseous monocyanoethylene, trans-dicyanoethylene, and allylcyanide have been measured at C1s and N1s edges using 2 keV electron collisions in quasi-dipolar excitation conditions and the electron energy loss spectroscopy. The energy resolution has allowed the observation of transitions from different carbon sites. Ab initio calculations have been made to help the assignment of the experimental features. The spectra below the core-electron ionization limit have been interpreted in terms of transitions to the lowest-energy valence unoccupied molecular orbitals shown to be of pi* type in each molecule. The effects of the conjugation between the multiple bonds on the spectra and on the splitting of the pi* type molecular orbitals have been discussed. Strong electronic relaxation effects have been evidenced.