Molecular Association in Binary Mixtures of tert-Butyl Alcohol−Water and Tetrahydrofuran−Heavy Water Studied by Mass Spectrometry of Clusters from Liquid Droplets

The cluster structures observed by means of mass spectrometry for binary mixtures tert -butyl alcohol (TBA)−H 2 O and tetrahydrofuran (THF)−D 2 O with varying mixing ratios exhibit striking contrast, even though both TBA and THF are miscible with water at any mixing ratio. In the TBA−H 2 O mixtures at TBA mole fractions of ( X TBA ) ≤ 0.01−0.025, some of the H 2 O molecules in the H 2 O clusters are replaced by TBA molecules. For 0.01−0.025 ≤ X TBA ≤ 0.2−0.3, the self-aggregation of TBA forms dominant cluster structures, and the hydrogen-bonded water clusters are disintegrated with increasing X TBA . This TBA self-aggregation is reduced with further increasing TBA at X TBA ≥ 0.3. However, in the THF−D 2 O mixtures, THF molecules have a weak additional interaction with D 2 O clusters, and the self-aggregation of THF is not promoted in the THF−D 2 O mixtures. The D 2 O clusters still exist, even at a THF mole fraction of X THF = 0.3. On the basis of the observed cluster structure, the mechanism for the mixing between water and the organic solvent and the controlling factors in the self-aggregation are proposed.