The crossed molecular beam technique is used to study the formation of negative ions in monosubstituted halobenzenes, by electron transfer collisions, using potassium atoms as electron donor projectiles, in a collision energy range from 10 up to 500 eV. The negative ions are detected by time-of-flight mass spectrometry and a quasidiatomic dynamical behavior in the fragmentation is found. A minor negative fragmentation of the phenyl ring is also reported. The parent negative ion is not observed for the range of collision energies in use. Density functional theoretical calculations support the major abundance of the halogen negative ions and explain the completely different behavior in the negative fragmentation of these aromatic systems compared to the one previously observed with the three fluoro-iodo-benzene isomers.