In the present report we have studied the interactions of water with organic molecules possessing a functional group of an ether or a carbonyl group in solution in a hydrophobic medium or n-heptane at various concentrations. The infrared spectrum of the water in the water-organic molecule complex, which was clearly separated by a skillful subtraction method, drastically changed depending on the concentration of the solution. Analysis of the infrared spectrum has made clear the following. Water is hydrogen-bonded, by one OH only, to a functional group, with the other OH free, to form a one-bonded complex, when a functional group is isolated from the other in the hydrophobic medium. On the other hand, each OH of a water molecule is hydrogen-bonded to a functional group to form a two-bonded complex, when two or more of the group are within the interactive vicinity via water. The hydrogen-bonding structure of the complex was supported by the normal frequencies calculated by the ab initio quantum mechanical method. The present study has demonstrated that the hydrophobic isolation method combined with infrared spectroscopy (HIIR) is useful to study basic interactions of water with organic molecules under soft conditions.

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