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Significant deviations were found between the solution enthalpy in benzene at 298.15 K and the fusion enthalpy at the melting temperature of 1,2,3,4-tetraphenylnaphthalene (3.9 ± 0.5 kJ mol−1 and 23.6 ± 0.6 kJ mol−1 (470.8 K), respectively) and 1,3,5-triphenylbenzene (20.1 ± 0.2 kJ mol−1 and 32.4 ± 1.2 kJ mol−1 (447.3 K)). These aromatic compounds are structurally related to benzene and their solution enthalpies in hypothetical liquid state at 298.15 K in benzene should be close to zero, so the differences between the solution enthalpy of crystal and the fusion enthalpy at the melting temperature should be attributed to the temperature dependence of the fusion enthalpy. Direct adjustment of the fusion enthalpy to 298.15 K requires knowledge of the supercooled liquid state heat capacity, which is hardly attainable by conventional methods due to fast crystallization. The heat capacities of 1,2,3,4-tetraphenylnaphthalene and 1,3,5-triphenylbenzene in liquid, deeply supercooled liquid, glassy and crystalline states were obtained for the first time by using fast scanning calorimetry in wide temperature ranges. Crystalline 1,2,3,4-tetraphenylnaphthalene heat capacity was measured over the temperature range from 323 to 410 K by conventional DSC. The temperature dependences of the heat capacities of the studied compounds in supercooled liquid state were fitted with the linear equations. The experimental results obtained by fast scanning calorimetry are in excellent agreement with the data obtained by solution calorimetry and conventional DSC.

This work is devoted to the quantitative study of hydrogen bond formation of N-alkyl substituted ionic liquids with proton acceptor and proton donor organic solvents. 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [BMIM][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO], 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], triethylsulfonium bis(trifluoromethylsulfonyl)imide [Et3S][NTf2], 1-butyl-3-methylimidazolium tricyanomethanide [BMIM][TCM], 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4] were investigated by solution calorimetry and FTIR-spectroscopy techniques. The stretching vibration region of C O group of 2-pentanone in mixture with N-alkyl substituted ionic liquid in inert solvent carbon tetrachloride was analyzed at different concentrations of components for the estimation of proton donor ability of ionic liquids. Also, the stretching vibration region of the OH-group of methanol was studied in a ternary system carbon tetrachloride (inert solvent), methanol (proton donor) and N-alkyl substituted ionic liquid for the estimation of proton acceptor ability of ionic liquids. The hydrogen bond enthalpy of methanol in ionic liquids was calculated using data of measured solution enthalpies and data extracted from the literature. The frequency shifts of the OH-group of methanol induced by intermolecular interactions within ionic liquids in a carbon tetrachloride solution were compared with the hydrogen bonding enthalpies of methanol with ionic liquids. A linear relationship between the frequency shifts of the OH-groups and hydrogen binding enthalpies of methanol in ionic liquids were found. According to measured FTIR-spectroscopy data, the N-alkyl substituted ionic liquids analyzed in this work possess weak proton donor properties, and at the same time their proton acceptor ability (basicity) is much higher and shows dependency on anion structure.

In this work, we have studied the thermochemistry of the hydrogen bond formation between ionic liquids and solute molecules. The solution enthalpies of several organic compounds (benzene, acetone, 3-picoline dimethylsulfoxide, formamide, N-methylformamide, acetamide, N-methylacetamide) in the series of ionic liquids with common anion bis(trifluoromethanesulfonyl)imide and different cations (1-butyl-3-methylimidazolium [BMIM][NTf2], 1-butyl-1-methylpyrrolidinium [BMPYR][NTf2], 1-butylpyridinium [BPY][NTf2], 1-butyl-1-methylpiperidinium [BMPIP][NTf2], trimethylpropylammonium [TMPAm][NTf2]) were measured by solution calorimetry at infinite dilution. The enthalpies of hydrogen bond between solutes and ionic liquids were determined by the previously proposed approach. The hydrogen bond enthalpies were correlated with the proton acceptor ability of ionic liquids from the Kamlet-Abboud-Taft equation and the proton donor ability of amides from the Abraham model. The proton donor ability and hydrogen bond reorganization of studied ionic liquids was analyzed. The formation of the hydrogen bond complexes of linear amides with ionic liquids with different compositions was shown. The effect of the ionic liquid structure on the strength of the hydrogen bond of linear amides with ionic liquids has been established.

This work continues the development of the additive scheme for the calculation of solvation enthalpies of aromatic compounds in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). In this study, heterocyclic aromatic compound were selected as solutes. The solution enthalpies of 14 heterocyclic aromatic compounds in [BMIM][BF4] were measured at 298.15 K. Based on the experimental and literature data, the solvation enthalpies of heterocyclic aromatic compounds in [BMIM][BF4] were calculated. The contributions of the exchange of CH–group with –N=, >NH, >NCH3, –S–, and carbonyl >C=O substituent groups into the solvation enthalpies in [BMIM][BF4] were calculated. These values were compared with analogous contributions in benzene. Solvation enthalpies of heterocyclic aromatic compounds in [BMIM][BF4] calculated by the additive scheme were compared with experimental values, revealing a good agreement between calculated and experimental data. This fact indicates that group additive scheme for prediction of the solvation enthalpies can be successfully applied to heterocyclic aromatic compounds in ionic liquids.