= Solution
\b[Transfer is favourable when new <water>–solute interactions compensate the cavity and reorganization costs of accommodating the solute.] The <Gibbs energy> also includes the loss of solute–<alkane> interactions; it is not simply a count of <hydrogen bonds>. <isobutane> cannot compensate those costs with strong directional interactions, explaining its positive <transfer Gibbs energy>. <acetone> and both <amines> can accept <hydrogen bonds> from <water> and have favourable electrostatic <solvation>, making their transfer moderately favourable. <isopropylamine> can additionally donate to <water>, consistent with a somewhat greater preference for <water> than <trimethylamine>.
<acetamide> combines a strong <carbonyl> acceptor with N–H donors and has the most favourable hydration in the group, accounting for its much more negative <transfer Gibbs energy>. Its pure solid lattice is not an extra sublimation penalty to insert here: the stated process starts from a dilute <alkane> solution and ends in dilute <water>, rather than dissolving the pure crystal. The nonmonotonic relationship between <hydrogen-bond acceptor parameter> and <transfer Gibbs energy> is expected because donor strength, nonpolar surface, <solvent cavity formation>, and all other <solvation> contributions also enter.
For matched <standard states>, $\Delta G^\circ_{\mathrm{tr}}=-RT\ln K_{\mathrm{tr}}$, with $K_{\mathrm{tr}}$ the <water>-to-<alkane> activity ratio. As an illustrative 298 K calculation, the <hydrocarbon> value implies $K_{\mathrm{tr}}\simeq7.0\times10^{-4}$, whereas the <amide> value implies approximately $3.6\times10^4$. These are standard-state partition preferences, not absolute aqueous solubilities. <amine> <protonation> could introduce an additional pH-dependent contribution to an experimentally measured <distribution coefficient>, but no such speciation information is supplied and it is not needed for the molecular comparison.
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