"Identification of Hydrogen-Bonded Oligomers in Associating Liquid by 1H NMR: 1-Phenyl-1-cyclohexanol",
Bulletin of the Chemical Society of Japan, 86, 569-576 (2013).
Non-monotonous temperature dependence, which suggests formation of closed oligomer(s) via hydrogen-bonds, is detected in heat capacity and dielectric constant of the title compound in the liquid state. The 1H NMR signal of hydroxyl protons showed a temperature-dependent fine structure. Quantum-chemical calculations on oligomers of several types revealed that the fine structure is plausibly interpreted as a temperature-dependent formation/destruction of oligomers. A coherent analysis of calorimetric, FT-IR, dielectric and 1H NMR results shows that the neat liquid of the title compound consists mostly of closed (square) tetramers via H-bonds at lower temperatures, and oligomers with open (or straight) H-bonding and non H-bonding (monomer) at higher temperature.
"Calorimetric and Spectroscopic Evidence of Chain-Melting in Smectic E and Smectic A Phases of 4-Alkyl-4'-isothiocyanatobiphenyl (nTCB) ",
J. Phys. Chem. B, 116, 9255-9260 (2012).
To confirm the molten state of the alkyl chain in soft crystalline phase, smectic E (SmE) phase, thermodynamic and spectroscopic analyses were performed on 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n: the number of carbon atoms in the alkyl group). DSC results of 11TCB and 12TCB, having extra smectic A phase besides smectic E phase, show that their chain-length dependence of entropies of transition (ΔtrsS) from the ordered crystalline (OC) phase to the SmE phase matches the trend found for nTCB (n = 4-10), while no chain-length dependence is observed in ΔtrsS at the SmE-to-SmA and SmA-to-isotropic liquid (IL) phase transitions in 11TCB and 12TCB. Temperature dependences of FT-IR spectra of six compounds (n = 2, 3, 5, 8, 10, and 12) were recorded. The CH stretching modes of the chain exhibited more pronounced change at the transition from the OC to the SmE phase than at the transition from the SmE phase to the IL or SmA phase. These results indicate that the alkyl chain is molten in the SmE phase as in IL. The disordering process of nTCB molecules from the OC to IL via anisotropic mesophases is discussed in terms of entropy.
"Calorimetric Study of Glass Transition in Molecular Liquids Consisting of Globular Associates: Dicyclorohexylmethanol and Tricyclohexylmethanol",
J. Phys. Chem. B, 116, 3938-3943 (2012).
Heat capacities of liquids and liquid-quenched glasses (LQGs) of dicyclorohexylmethanol (DCHM) and tricyclohexylmethanol (TCHM) were measured by adiabatic calorimetry. Upon cooling the liquid compounds, they undergo glass transitions around 250 and 265 K, respectively. Temperature dependence of the FT-IR spectrum of TCHM liquid showed the gradual formation of dimers in the supercooled state with decreasing temperature. The magnitude of heat capacity jump at glass transition is discussed through a comparison with other low-molecular mass LQG. Combining the present results with previous heat capacity results on crystalline TCHM, residual entropies of LQG and standard thermodynamic quantities are established for both compounds.
"Entropic Contribution of Flexible Terminals to Mesophase Formation Revealed by Thermodynamic Analysis of 4-Alkyl-4'-isothiocyanatobiphenyl (nTCB)",
J. Phys. Chem. B, 114, 4870-4875 (2010).
To understand the role of intramolecular degrees of freedom in forming mesophases, thermodynamic analysis was performed for 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n is the number of carbon atoms in the alkyl group), which exhibits the crystal E (CrE) phase as a mesophase. The heat capacities of 2TCB and 5TCB were measured by adiabatic calorimetry. Their entropies of transition (Δ trsS) were compared with those of other nTCBs (n ≤ 10). ΔtrsS of the phase transition from the ordered crystal to CrE phase increased with their alkyl chain length, whereas that of fusion of the CrE phase remained essentially constant. These behaviors clearly show that the alkyl chain of nTCB is fully disordered even in the CrE phase. Through the comparison of ΔtrsS among 5TCB, 4-pentyl-4'-cyanobiphenyl (5CB), and pentylbiphenyl, the role of the alkyl chain for the formation of mesophases is discussed.
"Neat Liquid Consisting of Hydrogen-Bonded Tetramers: Dicyclohexylmethanol",
J. Phys. Chem. B, 113, 10077-10080 (2009).
Nonmonotonous temperature dependence was detected in the heat capacity and dielectric constant of the title compound in the liquid state. A coherent analysis of FT-IR spectra, heat capacity, and dielectric constants shows that the neat liquid at low temperatures consists of closed (square) tetramers via H-bonds.
"Calorimetric and Dielectric Study of Organic Ferroelectrics, Phenazine-Chloranilic Acid, and Its Bromo Analog",
J. Chem. Phys., 130, 034503(1-7) (2009).
The heat capacities of single crystals of organic ferroelectric complexes phenazine-chloranilic acid (Phz-H2ca) and phenazine-bromanilic acid (Phz-H2ba) were measured. At temperatures below those of the reported ferroelectric phase transitions, heat capacity anomalies due to successive phase transitions were found in both complexes. Excess entropies involved in the low-temperature successive phase transitions are much larger than those due to the ferroelectric phase transitions. The temperature dependence of the complex dielectric constants showed the existence of multiple dielectric relaxation modes in both complexes and their deuterated analogs (Phz-D2ca and Phz-D2ba). We discuss the possibility of concerted hopping of neighboring protons within a hydrogen-bonded chain while taking into account the one-dimensional nature of the chain.
"Calorimetric Study of Correlated Disordering in [Hdamel]2[CuII (tdpd)2] · 2THF Crystal",
J. Phys. Chem. A, 112 (19), 4465-4469 (2008).
The heat capacity of [Hdamel]2[CuII(tdpd)2] · 2THF was measured from 6 to 250 K by adiabatic calorimetry. There are four heat anomalies around 150 K associated with disordering in the orientation of the uncoordinated THF molecules and in the conformation of the out-of-plane allyl groups of [Hdamel]+ units. The total entropy of transition was determined to be 19.8 J K−1 mol−1, less than the 4R ln 2 (R = gas constant) expected from the crystal structure at room temperature. The smallness of the total entropy change on phase transitions proves the presence of the strong motional correlation between the adjacent allyl groups. The calorimetric conclusion agreed with the crystal structure at 200 K re-examined in this study.
"One-Dimensional Correlation in the Dipolar Ising Crystal Tricyclohexylmethanol: Crystal Structure Revisited and Heat Capacity",
J. Phys.: Condens. Matter, 19, 176219(11pp) (2007).
The crystal structure of an organic weak-ferroelectrics, tricyclohexylmethanol (TCHM), was re-examined by single-crystal x-ray diffraction at room temperature. TCHM forms a dimer through hydrogen bonding at the centre of the dimer, where two hydroxyl groups are arranged in tandem and their direction is disordered in two possible orientations, which brings about a dipolar Ising nature. The heat capacity measured by adiabatic calorimetry from 6 to 400 K shows three anomalies including fusion at 368 K. The entropy of the ferroelectric transition is 1.9 J K−1 mol−1, supporting the order-disorder mechanism of dimer dipoles. A broad anomaly at 348 K is related to the breakage of the intra-dimer hydrogen bond. Detailed analysis of the temperature dependence of heat capacity due to the phase transition showed the presence of a broad hump in the excess heat capacity around 160 K. The temperature dependences of the excess heat capacity and the existing dielectric constant can be analysed in terms of a highly anisotropic Ising model.