Re. Barrans et al., Hydrogen bonding in aggregates of dialkyl-substituted diphosphonic acids and monofunctional analogues, SOLVENT EXT, 17(5), 1999, pp. 1195-1217
Hydrogen bonding of dialkyl-substituted diphosphonic acids in nonpolar (tol
uene and CCl4) and alcohol (I-decanol) solutions is examined. The compounds
are monomeric in l-decanol and dimeric or higher in nonpolar organic dilue
nts. Infrared spectroscopy and molecular mechanics calculations suggest tha
t the dimers of P,P'-di(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP])
and its straight-chain isomer, P,P'-dioctyl methanediphosphonic acid (H2DO
[MDP]), adopt rigid highly hydrogen-bonded structures such as C or D. The h
omologous P,P'-di(2-ethylhexyl) ethane- and butanediphosphonic acids, H2DEH
[EDP] and H2DEH[BuDP], respectively, adopt structures that are also intermo
lecularly hydrogen-bonded but more flexible. The effect on the P=O stretchi
ng vibration of increasing l-decanol concentration in the solvent differs f
or these compounds. In the case of H2DEH[MDP] and H2DO[MDP],;he frequency r
emains constant until all CCl4 has been replaced by the alcohol, then the P
=O stretching frequency shifts to a lower energy. In the case of H2DEH[EDP]
and H2DEH[BuDP], a gradual shift to higher energy occurs as the alcohol co
ncentration increases. The magnitude of the difference in the P=O stretchin
g frequencies between CCl4 and I-decanol solution is greatest for organopho
sphonic acids, less for organodiphosphonic acids, and least for organophosp
horic acids.