Results from solvophobic theory applied to methylene selectivity in reversed-phase HPLC

A significant amount of work has been previously dedicated to the understanding of methylene selectivity parameter. The conventional theory applied for this understanding was mostly based on the assumption that the difference in the Gibbs free energy of transfer from the mobile phase to the stationary phase is a constant for any two compounds in a homologous series that differ by a CH₂ group. In the present study, it is shown based on solvophobic theory that this assumption is indeed correct, but it provides a theoretical justification for it. Exemplification of the results of theory was obtained using the values for methylene selectivity (α(CH₂)) measured experimentally for seven different C18 chromatographic columns including two core–shell columns and using water and either methanol or acetonitrile as an organic component. Four different homologous series of compounds were used for evaluation. The study proved the theoretical prediction that the values for α(CH₂) obtained using different homologous series of compounds are only slightly different from those obtained using the toluene–butylbenzene series. Even using different homologous series, the same type of information regarding the columns comparison, and the changes in log α(CH₂) with the solvent composition was obtained.     

A straightforward algorithm to estimate the dead time in GC from the retention behavior of homologous series

Summary A new and very quick algorithm for the determination of the dead time t₀ in GC is described. It is based on the relationship between the carbon chain length n_c and the net retention time for homologous series. The shortcoming of former algorithms is overcome: it can also be applied if some not directly consecutive members of the homologous series are used for the calculation.     

The solubility of C<Subscript>70</Subscript> in <Emphasis Type="Italic">n</Emphasis>-alkanols-1 C<Subscript>1</Subscript>-C<Subscript>11</Subscript> over the temperature range 20–80°C

The isothermal (20°C) solubility of fullerene C₇₀ in solvents of the homologous series of nonbranched saturated alcohols C₁-C₁₁ and polythermal (20–80°C) solubility of fullerene C₇₀ in solvents of the homologous series of nonbranched saturated alcohols C₄-C₁₁ were studied. The corresponding solubility diagrams are presented and characterized.     

Solute Retention in Column Liquid Chromatography. V. the Column Dead Volume

Abstract

Methods of determination of the column void volume with two homologous series of solutes (alkyl-substituted aromatic hydrocarbons and phenyl-substituted aliphatic alcohols) are considered in terms of correlation coefficients r of plots of log V'_R against carbon number over the temperature range 10[ddot]-30[ddot]C. The homologous series methods provide self-consistent fits as well as temperature-invariant data for the aromatic hydrocarbons, but not for the alcohols, for which a mixed retention mechanism is said to obtain. A new graphical method of determining the best-fit value of V_A is introduced that makes use of plots of r against assumed V_A. In contrast to work reported elsewhere by others, each of the series of compounds studied in this work clearly exhibits a maximum. Those for the aromatic hydrocarbons are temperature-invariant; however, this is not so for the alcohols, which is taken as evidence of thermal and/or multiple sorption interactions of these solutes with the stationary phase.     

Similarities in the Intensities of Analogous Rydberg–Rydberg Transitions in the Molecular Series CF x Cl y (x=3, 2, 1; y=1, 2, 3)

In this work, the photoabsorption behaviour of the molecular series CF₃Cl, CF₂Cl₂ and CFCl₃, involving their ground state and two different Rydberg series, has been studied. The discrepancies or similarities in the intensities of homologous transitions in the three CF _x Cl _y molecules have been analysed on account of their electronic structure. Absorption oscillator strengths have been calculated with the Molecular quantum defect orbital (MQDO) approach. Electronic transitions between states belonging to two different unperturbed Rydberg series of the same molecule have been calculated by us for the first time. The quality of the achieved oscillator strengths has been assessed by comparison with, to our knowledge, scarce experimental data available in the literature, through analysis of the discrepancies or similarities in the intensities of homologous transitions in the molecular series CF _x Cl _y when states of different type are involved, and by testing the compliance of regularities by the Rydberg series object of our study.Article for the special issue dedicated to J.-P. Malrieu     

The influence of the size and position of the alkyl groups in alkylimidazole molecules on their acid‐base properties

Dissociation constants of HL⁺ acids, where L stands for 1‐alkylimidazole, 1‐alkyl‐2‐methylimidazole, 1‐alkyl‐2‐ethylimidazole, 1‐alkyl‐2‐propylimidazole, 1‐alkyl‐4‐methylimidazole and 1‐alkyl‐2‐ethyl‐4‐methylimidazole, were determined potentiometrically. For each of the homologous series of these bases, a relationship has been derived between the pK_a value and the number of carbon atoms in the hydrocarbon group for (CH₂)_n ≤ 13. The basicity of the alkylimidazoles has been found to increase linearly with increasing carbon chain length. The slopes of straight plots of pK_a = f(n_CH2) have been found to increase with increasing basicity of homologous series of the alkylimidazoles.     

The solubility of fullerene C70 in monocarboxylic acids C n − 1H2n − 1COOH (n = 1–9) over the temperature range 20–80°C

The isothermal (20°C) solubility of fullerene C₇₀ in solvents of the homologous series of monocarboxylic acids C _{n ? 1}H_{2n ? 1}COOH (n = 1–9) and polythermal solubility over the temperature range 20–80°C of fullerene C₇₀ in solvents of the homologous series of monocarboxylic acids C _{n ? 1}H_{2n ? 1}COOH (n = 4–9) were studied. The corresponding solubility diagrams were obtained and characterized.     

Mesophase stability of new Schiff base ester liquid crystals with different polar substituents

Four new groups of Schiff base ester liquid crystal compounds, 4-((4?-substituted phenylimino) methyl)phenyl–4″-alkoxybenzoates, In_a–d, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the polar substituent X (CH₃O, CH₃, H, and Cl). Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10, and 12. Molecular structures of the prepared compounds were confirmed via FT-IR, ¹H NMR, mass spectroscopy, and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry and polarised light microscopy. Comparative studies between the present series and previously investigated 4-(4-substituted phenylazo)phenyl 4″-alkoxybenzoates revealed that the phenylimino mesogenic core increases the mesophase stability rather than the azo analogues.     

Electro-optical investigations and effect of asymmetry in bent-core liquid crystals

We report the synthesis and mesomorphic properties of a homologous series (10a–10g) of bent-core molecules constructed through covalent linkage of structurally non-symmetrical rod-like mesogens connected with a 1, 3-phenylene unit. The study of homologous series underlines the importance of length and nature of terminal chains. The homologues of shorter chains show a typical non-switchable rectangular columnar B₁ phase, while the switchable lamellar (B₂) phase is induced on moving to higher homologues. X-ray diffraction patterns indicate the presence of B₁ and B₂ mesophases. Polarised optical microscopy investigations under electric field in the B₂ phases revealed the existence of anticlinic antiferroelectric texture. The measured spontaneous polarisation value in one of the compounds is 936 nC cm^?2, a high polarisation value in bent-core liquid crystals.     

Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

New mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G₁–G₁₁), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and elemental analysis. The liquid crystalline properties of the series G_n and their precursory F_n were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series G_n were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (G_n) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G₁ and G₂) did not show any liquid crystalline behaviour, the homologous (G₃–G₁₀) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G₁₁), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.     

Mass spectrometry of 1,3,4-thiadiazolo thiacrown ethers

The mass spectra of two homologous series of 1,3,4-thiadiazolo thiacrown ethers possessing one or two heterocyclic subunits, respectively, have been correlated and compared with those of closely related open-chain analogues. The prevailing feature in the spectra of these macrocycles is the presence of homologous series of ions, which formally correspond to the sequential loss of C₂H₄O units from appropriate precursors. The majority of these ions have been rationalized in terms of structure and mechanism of formation by assuming an electron impact induced isomerization process (via H migration) of the molecular ion to several competing linear structures prior to fragmentation. Metastable peak analysis and high-resolution measurements provide support for the postulated fragmentation mechanisms and product ion structures.     

The influence of cyclic alcohols on the temperature of maximum density of water

The effect of a homologous series of cyclic monohydric alcohols (C₄−C₈) on the temperature of maximum density of water has been examined. The structural contribution to the shift in the temperature of maximum density (TMD) is positive (increased structuredness) for alcohols up to C₆ but becomes negative at C₈. The behavior is compared with that of linear monohydric alcohols and Ω-diols.     

Vergleichende Untersuchung der Bürzeldrüsenlipide von Möwen. Zusammensetzung der Bürzellipide der Lachmöwe (Larus ridibundus), Heringsmöwe (Larus fuscus) und Silbermöwe (Larus argentatus)

The uropygial gland fats from the black-headed, the lesser black-backed and the herring gull, investigated by GLC/MS-combination technique, are shown to be complex mixtures of ester waxes. Among the wax acids octanoic acid is the main component, followed by homologous series of 2-methyl-, 2,6-, 2,8-, 2,10- and 2,12-dimethyl- as well as 2,4,8-, 2,6,8-, 2,6,10- and 2,6,12-trimethyl substituted fatty acids with chain lengths from C₈-C₁₅. As alcoholic components homologous series of primary alkanols without and with methyl-substitution in 2-, 4-, 2,6-, 2,8-, 2,10-, 2,12-, 2,6,10- and 2,6,12-position and chain lengths from C₁₁-C₁₈ could be detected.     

Stationary phase effects in reversed-phase chromatography II. Substituent selectivities for retention on various hydrocarbonaceous bonded phases

Summary Linear free-energy relationships are manifest in the linear dependence of the logarithmic retention factor on the carbon number for homologous series in reversedphase chromatography and allow the comparison of the free-energy increments of substituents for retention of a given elute by different stationary phases. Three methods were used for such comparison. In the first two, methylene group selectivities obtained from retention data obtained with homologous series on different hydrocarbonanceous bonded phases were compared by using different approaches. In the third method the energetics of retention of the end groups such as phenyl-, bromo- and disulfide-moieties of homologous series were examined. The results show that at fixed mobile phase composition and temperature the free energy increments due to methylene groups upon retention by alkyl-silica stationary phases are identical. Only hydrocarbonaceous bonded phases with short (C₁–C₂) alkyl chains or functional groups of unusual shape show consistent differences from octyl- or octadecyl-silicas. The results broaden the theoretical basis for the development of quantitative structure-retention relationships to be used for the prediction or interpretation of retention data in reversed-phase chromatography.Part I: ref. [23]Dedicated to Professor István Halász for his six tieth birthday.     

Dielectric studies of the 4-n-alkyl-4'-thiocyanatobiphenyl (nBT) homologous series (n=2-10) in the isotropic and E phases

Results of the dielectric studies of nine members of the nBT (4-n-alkyl-4'-thiocyanatobiphenyl, n= 2-10) homologous series in the crystal E (E) and isotropic (I) phases are presented. The dependence of the static permittivity ?_s in the isotropic phase, the longitudinal relaxation times τ_is and τ_∥, and the activation enthalpies ΔH _is and ΔH _∥ on the number of carbon atoms in the alkyl chain n are analysed. A considerable increase in the retardation factor g= τ_∥/τ_is with decreasing n is observed. The results are compared with those obtained for similar two-ring homologous series. The parameters characterizing the molecular rotations around the short axis in the E phase (τ_∥ and ΔH _∥) indicate a hardening of this solid-like phase with shortening of the alkyl chain.     

The influence of terminal group and repeat unit structure on mass-mobility correlations observed for homologous series

Mass-mobility correlations were investigated by ion mobility-mass spectrometry (IM-MS) for 11 structurally-unique homologous series composed of commercially-available compounds. Structural variation involved the inclusion of different repeat units (i.e., glucose, propylene glycol, or ethylene glycol) in oligomeric series and different terminal groups in CH₂-homologous series. Terminal group structures included both aliphatic and aromatic acids, as well as aliphatic and aromatic amines. Mass-mobility correlations were also investigated for select CH₂-homologous series identified in a pyrolysis bio-oil and compared with results observed for commercial series. A linear mass-mobility correlation (R ² ≥ 0.996) was established for all series except those in which a substantial change in the gas-phase conformation of ions was probable. Slopes observed for CH₂-homologous series with a single terminal group were significantly steeper than slopes observed for series containing two terminal groups. Additionally, a correlation between slope and double bond equivalents (DBE) suggested that the CH₂-homologous series identified in bio-oil were structurally similar to commercial series containing two terminal groups.     

Synthesis and mesomorphic properties and optical behaviour analysis of homologous series azobenzene liquid crystal monomer with polar substituents

ABSTRACT

Twenty novel azobenzene liquid crystal micromolecular compounds named ω-[4-(p-substituted azobenzeneoxy carbonyl]acid (X-ABCnA) have been designed and synthesised, followed by studies on the thermal performance and mesomorphic properties of the compounds. The liquid crystal compounds were divided into five homologous series based on the terminal substituents R (R = CH₃O, CH₃, H, Cl, NO₂). In each series, the number of carbons on flexible chain was 4, 6, 8 and 10, respectively. Fourier-transform infrared, proton nuclear magnetic resonance and elementary analysis demonstrated that the structure of the synthesised azobenzene liquid crystal compounds was consistent with the molecular design. The mesomorphic properties were tested, analysed and characterised by using differential scanning calorimetry and polarised optical microscopy. The melting transition (T _m) of all the compounds in homologous series with different substituents appeared to decrease with the increase of carbon numbers on flexible chains. The same held true for the temperature of isotropic-mesophase/crystalline transition. The compounds with stronger polarity of terminal substituents were more likely to form broader mesogenic ranges. The liquid crystal compounds discussed in this work can be regarded as a reference for the synthesis of mesogenic arms participating in the synthesis of novel multi-arm liquid crystalline macromolecules and polymers.     

Determination of Vapor Pressures Using Extrapolation of Adjusted Retention Times

Vapor pressure is one of the fundamental properties which govern the distribution of organic compounds in the environment. This property is estimated for five series of homologous substituted alkanes of the type H—(CH₂)_n—Y, where Y denotes Cl, Br, CHO, COOCH₃, OCOCH₃ and n varies from 5 to 14 using extrapolation of adjusted retention times to 25 °C. The results are compared with those obtained by using indirect methods for 40 compounds and a significant improvement is obtained. Indeed, the absolute average error percentage for the same series does not exceed 2.6%     

The influence of an electrolyte on micelle formation in aqueous solutions of sodium monoalkyl sulfosuccinates

Critical micelle concentrations were determined by conductometry for the homologous series of sodium monoalkyl sulfosuccinates ROOCCH₂CH(SO₃Na)COONa (R is an alkyl radical, C₁₀–C₁₅) in the presence of sodium chloride. Coefficients of the Corrin-Harkins equation were calculated. It was shown that the formation of micelles began when a certain value of the mean ionic activity of the surface active substance was reached.     

Thermotropic mesomorphism of mixed-valent diruthenium aliphatic carboxylates with axial anion bearing two aliphatic chains

A homologous series of binuclear mixed-valent diruthenium tetracarboxylates, Ru₂(O₂C(CH₂)_n?2CH₃)₄DHDP (DHDP = di(hexadecyl)phosphate axial anion, n = 10, 12, 14, 16, and 18), have been synthesized and characterized, and the liquid crystalline properties of these compounds were examined. All the compounds exhibit a room-temperature crystalline lamellar phase and a high temperature (above 140°) Col_h mesophase. Another, probably semi-crystalline, lamellar intermediate phase has also been found for all the studied compounds but for the n = 18 derivative. Comparison with related mesogenic homologous series where the equatorial ligands are also linear carboxylates, but the axial anions bear just one aliphatic chain (carboxylates, octylsulfonate, and dodecylsulfate), shows that the presence of a second aliphatic chain in the axial anion both lowers the transition temperatures and modifies the nature of the intermediate lamellar phase. Structural models at the molecular level are suggested for the crystalline lamellar and the Col_h phases.