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The application of FTIR spectroscopy to concentrated solutions of tetrolic acid shows, for the first time, a direct relationship between molecular self association in solution and H-bonded motifs in the subsequently crystallised solid phases.

Abstract. There has been much recent interest in the role of solution chemistry and in particular the importance of molecular self-assembly in the nucleation of crystalline phases.Techniques such as FTIR and NMR have highlighted the existence of solution phase dimers which in many cases mirror the structural synthons found in the resulting macroscopic crystals. However there are no reported examples in which this new insight into the solution phase has been linked directly to the kinetics of crystal nucleation. Here for the first time, using a combination of solution FTIR, computational chemistry and measured crystal nucleation rate data, such a link is demonstrated for p-aminobenzoic (PABA) and benzoic acids nucleating from polar and nonpolar solvents. Solute dimerization and desolvation are found to be rate determining processes in the overall nucleation pathway.

Little is known concerning the precise molecular pathway that links fluid-phase molecules to those in nascent crystal nuclei. In this paper the process of molecular self-assembly has been studied in concentrated solutions using FTIR spectroscopy. Three carboxylic acids, benzoic, tetrolic, and mandelic acids, have been chosen on the basis of their differing crystal chemistries, as reflected in observed hydrogen-bonding motifs. Using the solid-state spectra as a means of unambiguous assignment of carboxyl and hydroxyl vibrations associated with hydrogen bonding, spectroscopic data are reported for solutions as a function of both composition and solvent. In the cases of benzoic acid and tetrolic acid, a link between the growth synthon and the structural synthon is apparent. Mandelic acid, on the other hand, provides a more complex case in which strong solvation effects are evident, leading to the conclusion that significant molecular rearrangement must occur within the developing crystal nuclei.