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The clearest comparison is between the two amines, which have the same molecular formula and molar mass. isopropylamine can donate N–H hydrogen bonds to neighbouring nitrogen lone pairs; trimethylamine has no N–H donor. The resulting intermolecular association raises the primary amine's boiling point, allowing it to remain liquid at room temperature, whereas trimethylamine is gaseous. Independent phase-change data place their normal boiling points on opposite sides of room temperature.^[ref]

acetone has a substantial carbonyl dipole and London dispersion forces sufficient for a room-temperature liquid, even though it cannot build a strong donor–acceptor hydrogen bond network by itself. isobutane has mainly London dispersion forces and a compact shape and remains gaseous. acetamide combines carbonyl acceptors with two N–H donors, allowing an extended, directionally bonded crystal lattice; favourable packing as well as intermolecular association stabilizes its solid state.

These compounds have similar molar masses, so mass alone cannot explain the differences. The hydrogen-bond acceptor parameter also cannot predict the phase on its own: a pure substance needs complementary donors to exploit strong acceptor sites, and freezing additionally depends on crystal packing and entropy. A stronger acceptor does not automatically imply a higher melting point for arbitrary molecules.