HYDROGEN BONDING IN AGGREGATES OF DIALKYL-SUBSTITUTED DLPHOSPHONIC ACIDS AND MONOFUNCTIONAL ANALOGUES∗

ABSTRACT

Hydrogen bonding of dialkyl-substituted diphosphonic acids in nonpolar (toluene and CC1₄) and alcohol (1-decanol) solutions is examined. The compounds are monomeric in 1-decanol and dimeric or higher in nonpolar organic diluents. Infrared spectroscopy and molecular mechanics calculations suggest that 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 homologous P.P'-di(2-ethylhexyl) ethane- and butanediphosphonic acids, H₂DEH[EDP] and H₂DEH[BuDP], respectively, adopt structures that are also intermolecularly hydrogen-bonded but more flexible. The effect on the P=0 stretching vibration of increasing 1-decanol concentration in the solvent differs for these compounds. In the case of H₂DEH[MDP]and H₂DO[MDP], the frequency remains constant until all CC1₄ has been replaced by the alcohol, then the P=0 stretching frequency shifts to a lower energy.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 concentration increases. The magnitude of the difference in the P=0

Notes

Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences (dialkyl diphosphonic acids) and the Environmental Management Science Program of the Offices of Energy Research and Environmental Management (dialkyl phosphoric acids), U. S. Department of Energy, under contract number W-31-109-ENG-38.