FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE DETERMINATION OF LITHIUM CATION BASICITIES BY THE KINETIC METHOD - UPWARD EXTENSION OF THE SCALE TO PHOSPHORYL COMPOUNDS

Lithium cation basicities (LCBs) are reported for a series of 16 phosp horyl compounds, including phosphine oxides, phosphinates, phosphonate s and phosphates. The experiments were carried out using the kinetic m ethod applied to Fourier transform ion cyclotron resonance mass spectr ometry. Two different data treatments of the Napierian logarithm of io n peak intensity ratios were compared: extrapolation to zero kinetic e nergy and weighted averaging of data over the range of energies studie d. The effect of pressure on the LCB determinations was also studied. An increase in the pressure of the collision gas allows one to decreas e the collision energy necessary for efficient dissociation of the lit hium-bonded dimer, thus favoring the fragmentation pathway of lowest e nergy. Among the monofunctional ligands, the phosphoryl derivatives st udied have the largest LCBs yet known. The previously published self-c onsistent LCB scale of Taft and co-workers was extended upward by 14 k J mol(-1). (C) 1998 John Wiley & Sons, Ltd.