Enthalpy changes observed upon mixing liquid (R)- and (S)-enantiomers at 298.15 K

Enthalpies of mixing of (R)- and (S)-enantomers of liquid chiral compounds such as 5-isopropenyl-2-methyl- 2-cyclohexanone (1), glycerol acetonide (2), 4-isopropenyl-1-methylcyclohexene(3), 2,6,6-trimethyl-bicyclo[3.1.1] hept-2-ene (4) have been measured over the whole range of mole fractions at 298.15 K, albeit very small values. Mixing of R-1 and S-1 realises enthalpic stabilisation over the whole range of mole fractions, whereas that of R-2 and S-2, R-3 and S-3, or R-4 and S-4 realise enthalpic destabilisation over entire compositions. The maximum values of enthalpies of mixing and the intermolecular interaction of bond dipoles obtained by the molecular mechanics calculations showed a linear correlation, except the compound having two chiral centers or a phenyl group.