A molecular orbital study of monomeric metaphosphate. Density surfaces of frontier orbitals as a tool in assessing reactivity

Monomeric metaphosphates

“…A number of quantum mechanical calculations22, 23 have been made that purport to show that the monomeric metaphosphate ion is quite stable. [The statement in one paper that the kinetic barrier to the addition of a nucleophile to metaphosphate is low is at best irrelevant to the thermodynamic problem.]…”

“…An example of the work of the Australian investigators is the fragmentation of 2-chlorooctylphosphonate in the presence of terf-butyl alcohol to yield tert-butyl phosphate (eq 23). Phosphate esters of tertiary alcohols are C6H13CHC1CH2P032-+ (CH3)3COH -C6H13CH=CH2 + (CH3)3C0P03H-+ CP (23) not readily prepared by conventional means, and the simplest explanation for the preparation is that it proceeds by way of a fragmentation of the /3-halophosphonate to olefin, chloride ion, and P03" followed by electrophilic attack of the metaphosphate ion on the alcohol. Maynard and Swan, however, looked upon the reaction as a bimolecular process where terf-butyl alcohol participates in the fragmentation.…”

Hydration of monomeric metaphosphate anion in the gas phase

“…Interest in the monomeric metaphosphate anion P03" stems from its proposed intermediary role in phosphorylation and the hydrolysis of phosphate esters1 and generally from the importance of phosphates to the chemistry of biological systems.2 Interest in the combustion of phosphorus and phosphorus compounds as impurities in coal-fired magnetohydrodynamic generators has also motivated study of the P03" anion.3-5 Consequently, along with a basic interest in the bonding and electronic structure of phosphorus compounds, P03-has been the subject of several quantum mechanical treatments. [5][6][7][8][9] In particular, P03-affords valuable comparisons with its nitrogen congener N03-. A recent ab initio study6 of P03-with assumed Dlh symmetry indicates that the P-0 bond is highly polar with little double-bond character.…”

NMR Studies of the Mechanism of Enzyme Action

“…The dissociative mechanism involves the initial, rate-determining elimination of the leaving group (X) by lone pair electrons on the oxygens to yield the planar trigonal monoanion, monomeric metaphosphate, as an intermediate. This species, which is a highly reactive electrophile, due possibly to its large and overlapping cr* and v* LUMOs (lowest unoccupied molecular orbitals) that extend in all directions (25,26) rapidly binds the nearest nucleophile or entering group (Y). Evidence for the existence of metaphosphate consists of X-ray structures of isoelectronic species (27), its direct detection in the gas phase by mass spectroscopy (28), and its trapping as a reaction intermediate in aqueous solution (29,30).…”