Molecular polymeres of organic compounds could be identified with a special mass spectrometer by their negative ions without fragmentation from acetone, methanol, and formic acid. Verification of these measurements was obtained by the investigation of deuterated samples. Molecular ions were measured up to trimers. Benzene and cyclohexane did not show polymer ions. The measured pressure dependence indicates preference of electron attachment in ion production against ion molecule reactions. The complexes are held together by the intermolecular dipole forces.