Ethylene glycol (HO–CH₂–CH₂–OH) is used as automotive antifreeze. Consider an isolated pair of ethylene glycol molecules in the gas phase.
(a) For a single ethylene glycol molecule, identify the number of hydrogen-bond donors and the number of hydrogen-bond acceptors. Justify each identification with reference to atomic connectivity and lone-pair availability.
(b) Determine the maximum number of distinct hydrogen bonds that can form simultaneously between the two molecules. Clearly state which atoms serve as donors and which as acceptors for each bond.
(c) Explain why it is not possible for additional hydrogen bonds to form between the two molecules beyond the number you reported in part (b), even though multiple hydrogens and lone pairs remain present.