The enthalpies of dissolution in water at infinite dilution (i d), Delta H-tot(infinity), of propanal, butanal, 2-methylpropanal, pentanal, and 2,2-dimethylpropanal were measured by Isothermal calorimetry at T = 298 15 K. The enthalpies of solution, Delta H-sol(m)infinity, in water were derived by subtracting the enthalpies of the hydration reaction at 298.15 K from the measured enthalpies of dissolution The values obtained were combined with the standard enthalpies of vaporisation, Delta H-vap(m)infinity, to obtain the corresponding enthalpies of solvation at i d, Delta H-solv(m)infinity, The CH2 group contribution to Delta H-solv(m)infinity in water for linear aliphatic aldehydes was (-34 +/- 0.5) kJ mol(-1) in good agreement with the average value obtained for a large number of organic compounds containing linear alkyl chains. The simple additive method adopted to estimate the molar enthalpy of solvation at i d in water for the CHO functional group and its internal CO group gave (-28.1 +/- 1 5) kJ mol(-1) and (-22.5 +/- 1.5) kJ mol(-1), respectively. The enthalpies of solvation in heptane of linear and branched aldehydes with 3 to 11 C atoms were obtained using our earlier enthalpies of solution at i.d. and T = 298 15 K and recent experimental enthalpies of vaporisation from literature Methylene group contribution to Delta H-solv(m)infinity for linear aliphatic aldehydes in heptane was (-48 +/- 0 1) kJ mol(-1) Enthalpy of transfer from heptane to water for CH2 group was (2 1 +/- 0 4) kJ mol(-1) (C) 2010 Elsevier Ltd All rights reserved