The interaction of low-energy electrons with eight phthalates was studied using an electron monochromator-mass spectromer (EM-MS). Each phthalate captures electrons of discrete energy to yield negative ions by resonance or dissociative electron capture. Two negative ion resonances are generally observed for each ion. Electrons with energies of similar to 0.6 and similar to 1.1 eV result in maximum molecular ion intensity for o-phthalates, while higher energy electrons produce (M-R-1)(-), (M-R-1-R-2 + H)(-), and phthalic anhydride ions. In-Dimethyl phthalate yields a molecular ion with electrons of energies 0.19 and 0.87 eV, but no fragment ions. Electron attachment energies calculated with the HF/D95/HF/6-31G basis set and a scaling constant are in reasonable agreement with the experimental values for the first molecular ion state of each phthalate. Semiemperical calculations show that the optimum geometry for m-dimethyl phthalate results when both ester groups are coplanar with the benzene ring, while steric interactions force the ester groups of a-phthalates into noncoplanar orientations relative to the benzene ring. It is suggested that this geometry leads to efficient pi*-sigma* orbital interaction in the transient radical anion and facile fragmentation, producing product anions and radicals. Larger R groups result in a lowering of the electron energies required to produce (M-R-1)(-), a result which is interpreted on the basis of greater steric compression of the ester groups in the transient negative ion.