A) Enumeration of spectroscopically distinguishable water-ethanol dimers: Ethanol can occur in the trans (e t ), gauche+ (e g+ ) and gauche-(e g-) conformation. When acting as a hydrogen bond acceptor, it can offer its right (r) or left (l) lone electron pair. The nomenclature used in the article always implies the enantiomer engaging the right lone pair. When water (w) acts as the acceptor, it may engage its upper (u) or lower (l) lone electron pair. This results in the following dimer

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... ities, if we disregard water donor rotation around the hydrogen bond (2 achiral conformations and 3+2 chiral pairs, leading to a total of at most 7 spectrally distinguishable structures):