EXPERIMENTAL AND THEORETICAL INVESTIGATION OF GAS-PHASE COMPLEXES BETWEEN CHLORIDE-ION AND SOME CHLOROETHENES

Analysis of the negative ions produced from trichloroethene (TCE) and Z-1,2-dichloroethene (Z-1,2-DCE) in air at atmospheric pressure in an APCI source revealed the occurrence of the corresponding complexes wit h chloride ion. In contrast, under the same experimental conditions no such complexes were detected for E-1,2-dichloroethene (E-1,2-DCE) and tetrachloroethene (PCE). A bracketing approach and competition experi ments produced the following Cl--affinity scale: Z-1,2-DCE > TCE > PCE , E-1,2-DCE, benzene (39.3 kJ mol(-1)). The results of collision induc ed dissociation experiments on these (Cl-) (M) complexes suggest rathe r weak bonding interactions. Quantum chemical calculations at the; DFT Becke3-LYP level (B3LYP/6-311+G(d,p)//6-31+G(d)) support this conclus ion [the calculated binding energy (kJ mol(-1)) are: 58.6, 56.1, 43.5, and 15.1 for Z-1,2-DCE, TCE, E-1,2-DCE and PCE, respectively]. The ca lculations also show that such complexes are planar, with an almost li near C-H ... Cl- arrangement in the case of TCE and E-1,2-DCE. In cont rast, Z-1,2-DCE binds Cl- via both hydrogens to give a symmetric compl ex. A similar geometry is also predicted for the very weakly bound (Cl -)(PCE) complex. (C) 1998 Elsevier Science B.V.