Thermodynamics of fusion and sublimation for a homologous series of eleven alkane-α,ω-diols HO-(CH2)n-OH: Structure-related odd–even effect

Temperatures and enthalpies of fusion and solid-to-solid transition of a homologous series of linear alkane-α,ω-diols, HO-(CH₂)_n-OH where n = (6 to 16), were measured by differential scanning calorimetry (d.s.c.). The enthalpies and temperatures of fusion displayed a marked odd–even effect as a function of the number of methylene groups in the alkyl chains, with even terms showing higher values than odd terms. Thermodynamic parameters of fusion were compared with those of isoelectronic linear alkanes and earlier measured alkane-α,ω-diamines, alkane-α,ω-diamides and alkane-α,ω-dinitriles. Results were discussed with reference to the effects of chain length on crystal structures and packing patterns raised on hydrogen bonding and hydrophobic interaction interplay. The enthalpies of sublimation at T = 298.15 K were obtained from the enthalpies of fusion and the literature enthalpies of vaporisation, both adjusted to 298.15 K. A smoother odd–even pattern was observed for the enthalpies of sublimation.     

Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol,chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.     

Thermochemistry of some methoxypyridines

The standard (p^o = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for the liquids 2-methoxypyridine, 4-methoxypyridine and 2,6-dimethoxypyridine were determined by static bomb combustion calorimetry. The standard molar enthalpies of vaporization, at T = 298.15 K, were measured by Calvet microcalorimetry. The standard (p^o = 0.1 MPa) molar enthalpies of formation of the three compounds studied, in the gaseous phase, at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of vaporization, yielding ((−42.7 ± 1.9), (−18.2 ± 1.8) and (−233.5 ± 1.8)) kJ · mol⁻¹, for 2-methoxypyridine, 4-methoxypyridine and 2,6-dimethoxypyridine, respectively.     

Fusion and solid-to-solid transitions of a homologous series of alkane-α,ω-dinitriles

Fusion and solid-to-solid transitions of a homologous series of 11 alkane-α,ω-dinitriles NC-(CH₂)_n-CN, where n = (1 to 10 and 12), were investigated by differential scanning calorimetry (d.s.c.). The temperatures of fusion increased as a function of the number of carbon atoms in the alkyl chains and showed a marked odd–even effect with even terms displaying higher values. Molar and massic enthalpies and entropies of fusion also showed odd–even alternation. Solid-to-solid transitions were detected for all compounds, except dodecanedinitrile. Comparison was made with the literature values for temperatures, enthalpies, and entropies of fusion of linear alkanes and alkane-α,ω-diamines.     

Thermochemistry of Cu(II) and Ni(II) complexes with N,N-di-n-butyl-N′-thenoylthiourea and N,N-di-iso-butyl-N′-thenoylthiourea

Two substituted N-acylthioureas and the respective Ni(II) and Cu(II) complexes were synthesized, namely: N,N-di-n-butyl-N′-thenoylthiourea (Hnbtu); N,N-di-iso-butyl-N′-thenoylthiourea (Hibtu); bis[N,N-di-n-butyl-N′-thenoylthioureato]nickel(II), [Ni(nbtu)₂]; bis[N,N-di-n-butyl-N′-thenoylthioureato]copper(II), [Cu(nbtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]nickel(II), [Ni(ibtu)₂]; bis[N,N-di-iso-butyl-N′-thenoylthioureato]copper(II), [Cu(ibtu)₂]. The standard (p^° = 0.1 MPa) molar enthalpies of formation and sublimation of the two N-acylthioureas were measured, at T = 298.15 K, by rotating-bomb combustion calorimetry and Calvet microcalorimetry, respectively. The standard (p^° = 0.1 MPa) molar enthalpies of formation of the Ni(II) and Cu(II) complexes were determined, at T = 298.15 K, by high precision solution–reaction calorimetry. From the results obtained, the enthalpies of hypothetical metal–ligand and metal–metal exchange reactions, in the gaseous phase, were derived, thus allowing a discussion of the gaseous phase energetic difference between the complexation of Ni(II) and Cu(II) to 1,3-ligand systems with (S,O) ligator atoms.     

Gas chromatography–mass spectrometry study of hydrogen–deuterium exchange reactions of volatile hydrides of As,Sb, Bi,Ge and Sn in aqueous media

The H–D exchange processes in MH_n or MD_n hydrides (M = As, Sb, Bi, n = 3; M = Ge, Sn, n = 4) taking place when they are in contact with H₂O or D₂O solution at different pH or pD values (interval of pH = [0,13]) have been investigated using gas chromatography–mass spectrometry (GC-MS). MH_n or MD_n compounds were injected into the headspace of reaction vials (4–12 ml) containing 1–2 ml of buffered solution maintained under stirring or shaking conditions. The isotopic composition of the gaseous phase hydrides/deuterides was determined at regular intervals in the range of time 0–15 min. The MH_n or MD_n compounds were synthesized in separate vials and their purity was checked separately before injection into the reaction vials. The mass spectra were deconvoluted in order to estimate the relative abundance of each species formed following the H–D exchange process (AsH_nD_3−n , SbH_nD_3−n, BiH_nD_3−n, n = 0–3; GeH_nD_4−n, SnH_nD_4−n, n = 0–4) and the relative abundance of H and D. In the investigated pH (or pD) interval arsanes and stibanes undergo H–D exchange in alkaline media for pH > 7. No H–D exchange was detected for the other hydrides, where the prevailing process is their decomposition in the aqueous phase. A reaction model, based on the formation of protonated or deprotonated intermediates is proposed for H–D exchange of MH_n or MD_n compounds placed in contact with H₂O or D₂O at different pH or pD values. The H–D exchange in the already formed hydrides can be source of the interference in mechanistic studies on hydride formation performed using labeled reagents; no H–D exchange was detected within the following pH intervals that can be considered free from interference: arsanes pH = [0,7), stibanes pH = [0,7), bismuthanes, germanes and stannanes pH = [0,13].     

Combined experimental and computational thermochemistry of isomers of chloronitroanilines

The standard (p^° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of 4-chloro-3-nitroaniline and 5-chloro-2-nitroaniline, in the condensed phase, were derived from their standard molar energies of combustion, in oxygen, to yield CO₂(g), N₂(g), and HCl · 600H₂O(l), measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T = 298.15 K, were derived by means of the Clausius–Clapeyron equation. The Calvet microcalorimetry was also used to measure the standard molar enthalpies of sublimation of these compounds, at T = 298.15 K. The combination of the standard molar enthalpies of formation in the condensed phases and the standard molar enthalpies of sublimation yielded the standard molar enthalpies of formation in the gaseous phase at T = 298.15 K for each isomer. Further, the standard (p^° = 0.1 MPa) molar enthalpies, entropies and Gibbs free energies of sublimation, at T = 298.15 K, were also derived.The standard molar enthalpies of formation, in the gaseous phase of all the chloronitroaniline isomers were also estimated by the Cox scheme and by the use of computational thermochemistry and compared with the available experimental values.     

Excess properties and vapour pressure of (3-diethylaminopropylamine + n-alkanes)

The vapour pressures of liquid (3-diethylaminopropylamine (3-DEPA) + n-heptane) mixtures were measured by a static method between T = (303.15 and 343.15) K at 10 K intervals. The molar excess enthalpies H^E at T = 303.15 K were measured for the systems {3-DEPA + C_nH_2n+2 (n = 6, 7, 12)}. The molar excess Gibbs free energies G^E were obtained with Barker’s method and fitted to the Redlich–Kister equation. The Wilson equation was also used. Deviations between experimental and predicted G^E and H^E, by using group contribution UNIFAC (Gmehling version) model, were evaluated.     

Experimental thermochemical study of the enthalpies of formation and sublimation of isonicotinamide,picolinamide, nicotinamide,isonicotinamideN-oxide,and nicotinamideN-oxide. The dissociation enthalpies of the N–O bonds

The standard (p ^∘  =  0.1MPa) molar enthalpies of combustion in oxygen, at T =  298.15 K, for crystalline picolinamide (2-NH₂COPy), nicotinamide (3-NH₂COPy), isonicotinamide (4-NH₂COPy), nicotinamide N -oxide (3- NH₂COPyNO), and isonicotinamide N - oxide (4-NH₂COPyNO) were measured by static-bomb calorimetry. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. The standard molar enthalpies of sublimation, at T =  298.15 K, for the three pyridinecarboxamide isomers were measured by microcalorimetry and the standard molar enthalpies of sublimation for the two pyridinecarboxamide N -oxide compounds were measured by a mass-loss effusion technique. From the enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies D_m^oof the (N ⁺ – O ⁻ ) covalent bonds were derived. Comparison has been made with D_m^o(N–O) values in pyridine N -oxide derivatives.     

A DFT study on group III and V combined hexagonal clusters as potential building motifs for inorganic nanomaterials

A detail theoretical investigation on the structure and electronic properties of inorganic hexagonal units and their higher order derivatives comprising group III (B, Al and Ga) and V (N, P and As) elements is performed. A series of 45 clusters, formed by a linear combination of hydrogen saturated hexagonal motifs up to five units, (MY)_2n+1H_2n+4 (M = B, Al, Ga; Y = N, P, As; n = 1–5) are considered to look into their metal–insulator–semiconductor (MIS) behavior. It is evident from the present study that the arsenic doped group III hexagonal units clearly have a decisive role in forming semiconductor materials.     

Vapor pressure and enthalpy of vaporization of linear aliphatic alkanediamines

Vapor pressures and the molar enthalpies of vaporization of the linear aliphatic alkanediamines H₂N–(CH₂)_n–NH₂ with n = (3 to 12) have been determined using the transpiration method. A linear correlation of enthalpies of vaporization (at T = 298.15 K) of the alkanediamines with the number n and with the Kovat’s indices has been found, proving the internal consistency of the measured data.     

Standard molar enthalpies of formation of 2-furancarbonitrile, 2-acetylfuran,and 3-furaldehyde

The standard (p^° = 0.1 MPa) molar energies of combustion of 2-furancarbonitrile, 2-acetylfuran, and 3-furaldehyde were measured by static bomb combustion calorimetry; the Calvet high-temperature microcalorimetry was used to measure the enthalpies of vaporization of these liquid compounds. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of phase transition, as (106.8 ± 1.1) kJ · mol^?1, ?(207.4 ± 1.3) kJ · mol^?1, and ?(151.9 ± 1.1) kJ · mol^?1, for 2-furancarbonitrile, 2-acetylfuran, and 3-furaldehyde, respectively.Standard molar enthalpies of formation are discussed in terms of the isomerization ortho meta. Enthalpic increment values of the introduction of the functional groups –CN, –CHO, and –COCH₃ were also compared with some other heterocycles; i.e. thiophene and pyridine.     

A novel design of a temperature-controlled FT-ICR cell for low-temperature black-body infrared radiative dissociation (BIRD) studies of hydrated ions

A novel design for a temperature-controlled ICR cell is described for use in black-body infrared radiative dissociation (BIRD) studies of weakly bound systems like water clusters. Due to several improved design features, it provides a very uniform black-body radiation environment, and at the same time maintains efficient pumping for a low collision rate on the order of 10^?2 s^?1. At the lowest temperatures reached, nominally 89 K cell plate temperature, water evaporation effectively ceases, while intracluster reactions in V⁺(H₂O)_n with a small activation energy are still observed. BIRD rate constants for Ag⁺(H₂O)_n, n = 4–6, are shown in the temperature range T = 160–320 K. For n = 6, a linear Arrhenius plot with R² = 0.9943 is obtained without any calibration, confirming the suitability of the cell for quantitative BIRD studies.     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Enthalpies of formation and decomposition of nickel hydride and nickel deuteride derived from (p,c,T) relationships

Measurements of equilibrium hydrogen pressure as a function of hydrogen content and of temperature are a convenient way to determine the thermodynamic properties of metal–hydrogen systems. To date such studies have only been carried out for the systems at relatively low hydrogen pressure. We have developed a high-pressure apparatus capable of pressures up to 1.2 GPa and temperatures up to T =  450 K for the studies of equilibrium conditions in the Ni–H systems and the Ni–D systems in order to derive corresponding enthalpies of formation and decomposition. The results show that although the pressures at given temperatures are always higher for (Ni  +  D₂) than for (Ni  +  H₂), the values of enthalpies are almost identical within the experimental error. The enthalpies of the formation and decomposition of both systems derived from these studies are compared with calorimetric measurements carried out at high pressure. The difference between enthalpies of formation and decomposition for both systems reflect hysteresis, a common phenomenon in transition metal hydrides.     

Evidence of an odd–even effect on the thermodynamic parameters of odd fluorotelomer alcohols

A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF₃(CF₂)_nCH₂OH, with n = 5 to 9}, is reported in order to explore the effect of the successive introduction of –CF₂– groups into the molecule on the thermodynamic properties related to (solid + liquid, solid + gas, and liquid + gas) equilibria. An odd–even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.     

Experimental and computational thermochemistry of 1,4-benzodioxan and its 2-R derivatives

The standard molar energies of combustion, at T = 298.15 K, of crystalline 1,4-benzodioxan-2-carboxylic acid and 1,4-benzodioxan-2-hydroxymethyl were measured by static bomb calorimetry in an oxygen atmosphere. The standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in the gas phase at T = 298.15 K: 1,4-benzodioxan-2-carboxylic acid ?(547.7 ± 3.0) kJ · mol^?1 and 1,4-benzodioxan-2-hydroxymethyl ?(374.2 ± 2.3) kJ · mol^?1.In addition, density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets, 6-311G⁷ and cc-pVTZ, have been performed for the compounds studied. We have also tested two more accurate computational procedures involving multiple levels of electron structure theory in order to get reliable estimates of the thermochemical parameters of the compounds studied. The agreement between experiment and theory gives confidence to estimate the enthalpies of formation of other 2-R derivatives of 1,4-benzodioxan (R = –CH₂COOH, –OH, –COCH₃, –CHO, –CH₃, –CN, and –NO₂).     

DFT study of group 8 catalysts for the hydrophenylation of ethylene: Influence of ancillary ligands and metal identity

Computational methods are used to investigate catalytic hydrophenylation of ethylene using complexes of the type [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ [Y = Mp, n = 1; Y = Tp, n = 0; M = Ru or Os; L = PMe₃, PF₃, or CO; Mp = tris(pyrazolyl)methane; Tp = hydrido-tris(pyrazolyl)borate]. The conversion of ethylene and benzene to ethylbenzene with [(Y)M(L)(Ph)]ⁿ⁺ as catalyst involves four steps: (1) ethylene coordination, (2) ethylene insertion into the M–Ph bond, (3) benzene coordination, and (4) benzene C–H activation. DFT calculations form the basis to compare stoichiometric benzene C–H activation by [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ complexes to yield methane and [(Y)M(L)(Ph)(NCMe)]ⁿ⁺. In addition, starting from the 16-electron species [(Y)M(L)(Ph)]ⁿ⁺, potential energy surfaces for the formation of ethylbenzene are calculated to reveal the impact of modifications to the scorpionate ligand (Mp or Tp), co-ligand (L) and metal center (M).     

A study of α-cyclodextrin with a group of cationic gemini surfactants utilizing isothermal titration calorimetry and NMR

Isothermal titration calorimetry has been applied to determine the stability constants, stoichiometry, formation enthalpies, entropies, and Gibbs free energies for the complexes of α-cyclodextrin (α-CD) with a series of bis-quarternary ammonium surfactants, (C_nN)₂Cl₂ (n = 12, 14, 16), in aqueous solutions at 293.15 K. The observed stability constants of the complexes are very large. For these quite stable inclusion complexes, the stoichiometry of most stable complexes changes from 2:1 to 6:1 as the number of methylenes (–CH₂–) in each of the hydrophobic tail is increased from 12 to 16. According to the same change of the hydrophobic chain, both formation enthalpy and formation entropy evidently decrease. The results also indicate that the association processes are characterized by both favorable enthalpy changes and unfavorable entropy changes. Chemical shift data of all protons in the CD molecule, induced by the formation of the (α-CD + (C₁₂N)₂Cl₂) complexes have been determined by Proton NMR spectroscopy.     

Synthesis and characterization of organophosphine/phosphite stabilized N-silver(I) succinimide: crystal structure of [(Ph3P)3 · AgNC4H4O2]

Six organophosphine/phosphite stabilized N-silver(I) succinimide complexes of the type L_n · AgNC₄H₄O₂ (L = PPh₃; n = 1, 2a; n = 2, 2b; n = 3, 2c; L = P(OEt)₃; n = 1, 2d; n = 2, 2e; n = 3, 2f) have been prepared by reacting [AgNC₄H₄O₂], which can be synthesized from succinimide and excessive Ag₂O in boiling water, with triphenylphosphine or triethylphosphite in dichloromethane under a nitrogen atmosphere. These complexes were obtained in high yields and characterized by elemental analysis, ¹H, ¹³C{H} NMR, IR spectroscopy and thermal analysis (TG and DSC). The molecular structure of 2c has been determined by X-ray single crystal analysis, in which the silver atom is in a distorted tetrahedral geometry.