Hydrogen bonding phosphorus compounds

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11,125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects, hydrogen, in aromatic substitution reactions, 2,163... 

It is not wise to assert categorically that the initiating reaction is actually the hydrogen bonding between the fluorine atom (or oxygen atom in T.E.P.P., see below) of the phosphorus compound and the active hydrogen. It should be noted in support,... 

Especially, the subdivision in different hydrogen bond acceptor atom sets improves the performance of the SEN approach while a subdivision depending on the hydrogen bond donor atom showed only a minor improvement compared to the general fit of Reiher et al. Thus, the SEN approach has proven as a tool to investigate hydrogen bonds of, e.g., transition metal compounds (171,174-177), peptides (178), enzymes (179), DNA and RNA (173), molecular switches (180), ionic liquids (181,182), and rotaxanes (183). However, the SEN approach is not solely restricted to hydrogen bond detection. This approach can also be apphed to determine the covalent interaction between metal atoms (184) or phosphorus atoms (162,185). Therefore, it is suitable for different kind of interactions. 

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