Experimental and Theoretical Studies of the Proton Affinity of Fluoroboroxine*

The proton affinity of fluoroboroxine, FBO, is explored both experimentally and theoretically. Results of selected-ion flow tube measurements are reported for proton transfer reactions which place the proton affinity (PA) of FBO between those of ethylene and acetylene, PA(C2H4) > PA(FB0) > PA(C,H,), with PA(FB0) equal to 158 + 6kcalmoll’. FBOH’ is produced from the reaction of BF: with H,O and is observed to rapidly transfer a proton to H,O, ethylene, propylene, benzene, cb-2-butene, iso-butene and styrene but only to add to acetylene to form FBOH+ *C2H, at 296 _+ 2 K. The results of ab initio molecular orbital calculations on FBO and on isomers of FBOH+ are reported for the Hartree-Fock and the full second-order Moeller-Plesset levels of theory with the 6-31G ** basis set. Structure optimizations were performed at both levels of theory using gradient techniques in the GAUSSIAN 82 program. The proton affinity, corrected for zero-point and thermal energies, and including correlation energy, is computed to be 163.8 kcal mol-’ .