The stability of two small dicarboxylate dianions, (O2C-C=C-CO2)2- (AD2-) and (O2C-CH2CH2-CO2)2- (SD2-)has been studied in the gas phase using electrospray mass spectrometry, photoelectron spectroscopy, and ab initio calculations. Despite their similar charge-seperation and size, AD2- was observed abundantly, whereas SD2- was very difficult to detect. Our ab intio calculation predicts that AD2- has a D2d structure iwth 0.418 eV adiabatic and 0.69 eV vertical electron binding energies, compared to the experimental values of 0.30 (0.10) eV and 0.60 (0.10) eV, respectively. SD2- was found to have a C2h structure with a negative adiabatic electron binding energy (-0.086 eV). Our detailed theoretical ananlysis indicates that while the two excess charges in SD2- are completely localized on the terminal carboxylate groups, there is significant delocalization of the excess charges into the -CC-pi-type orbitals in AD2-. The D2d structure of the AD2- dianion allows each carbonoxylate to interact with one of the two perpendicular pi-type orbitals of the acetylene moiety, thus providing extra stabilization while minimizing the Coulomb repulsion.
Revised: May 30, 2002 |
Published: May 10, 2000
Citation
Skurski P., J. Simons, X.B. Wang, and L.S. Wang. 2000.Experimental and Theoretical Investigations of the Stability of Two Small Gaseous Dicarboxylate Dianions: Acetylene Dicarboxylate and Succinate.Journal of the American Chemical Society 122, no. 18:4499-4507.PNNL-SA-32859.