The electronic dynamic structure factor S(q,omega) of conjugated finite-size oligomers is computed using the time-dependent Hartree-Fock (TDHF) approach. The resonances observed in electron scattering are analyzed using the Bloch representation of the single-electron transition density matrices for the corresponding polymers. The separation of relative and center-of-mass motions of electron-hole pairs, which is expected to hold for infinite chains, is shown to apply even for relatively small molecules, paving the way for a band-structure picture of the quasiparticles. Signatures of the exciton coherence sizes in the momentum dependence of the structure factor are analyzed.