MOLECULAR COCRYSTALS OF CARBOXYLIC-ACIDS .13. SPECTRAL CHARACTERIZATION OF THE ADDUCTS OF TRIPHENYLPHOSPHINE OXIDE WITH SUBSTITUTED BENZOIC-ACIDS AND THE CRYSTAL-STRUCTURES OF THE 1 1 ADDUCTS WITH 2,4,6-TRINITROBENZOIC ACID AND 3,5-DINITROBENZOIC ACID

The 1: 1 adducts of triphenylphosphine oxide with the 2-, 3- and 4-nitro-, 3,5-dinitro-, and 2,4,6-trinitro-substituted benzoic acids have been prepared, and characterized by infrared and P-31 n.m.r. spectroscopy. The crystal structures of two of these adducts, (triphenylphosphine oxide-3,5-dinitrobenzoic acid) and (triphenylphosphine oxide-2,4,6-trinitrobenzoic acid), have been determined by X-ray diffraction. In all examples, the presence of single directed hydrogen bonds between the phosphoryl oxygen and the carboxylic acid proton is confirmed. For the X-ray structures, the O...O distances are 2.54(4) and 2.55(1) angstrom respectively. Solid-state P-31 n.m.r. spectroscopy has also proved a convenient technique for the detection of the presence of a single conformational adduct type in cocrystals.