The acetone - chloroform system is the classic textbook example of a negative-pressure azeotrope, i.e. the vapour pressures of the binary mixtures are lower than expected for ideal mixtures, the mixing is exothermic and the excess volumes of mixing are negative. These deviations from ideal behaviour are thought to originate from hydrogen-bonding interactions which are present in the mixtures but not in the pure liquids. Previous studies, based on thermodynamic data, IR spectroscopy and Monte-Carlo simulations, have suggested conflicting structures for the azeotropic clusters. The aim of the proposed work is to finally determine the composition, structure and concentration of these clusters. This could prove that interspecies association is indeed causing the negative-azeotrope behaviour. This study might also lead to further optimisation of the computer models of chloroform and acetone.