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 with 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 experiments 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 induced dissociation experiments on these (Cl-) (M) complexes suggest rather weak bonding interactions. Quantum chemical calculations at the; DFT Becke3-LYP level (B3LYP/6-311+G(d,p)//6-31+G(d)) support this conclusion [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 calculations also show that such complexes are planar, with an almost linear C-H ... Cl- arrangement in the case of TCE and E-1,2-DCE. In contrast, Z-1,2-DCE binds Cl- via both hydrogens to give a symmetric complex. A similar geometry is also predicted for the very weakly bound (Cl-)(PCE) complex. (C) 1998 Elsevier Science B.V.