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     

Correlations between Van der Waals' volume and retention index general equation applicable to different homologous series

Summary Correlations between retention index (R_I) and Van der Waals' volume (V_W) in homologous series of n-alcohols, n-aldehydes and esters are studied on the stationary phases Carbowax 1540 and squalane. Influence of functional groups is quantified and a method for obtaining one general equation, valid for an indeterminate number of homologous series, is proposed.     

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.     

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.     

Carbynehydridoruthenium Complexes as Catalysts for the Selective,Ring-Opening Metathesis of Cyclopentene with Methyl Acrylate

The first members of a homologous series of long-chain, multiply unsaturated esters were obtained upon selective ring-opening metathesis of cyclopentene with methyl acrylate [Eq. (a)]. The catalysts are cationic carbynehydridoruthenium complexes (e.g. L=OEt₂), which were prepared for the first time by protonation of hydridovinylideneruthenium compounds in the presence of L.     

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.     

Signal processing of GC-MS data of complex environmental samples: characterization of homologous series

Identification and characterization of homologous series by GC-MS analysis provide very relevant information on organic compounds in complex mixtures. A chemometric approach, based on the study of the autocovariance function, EACVF_tot, is described as a suitable tool for extracting molecular-structural information from the GC signal, in particular for identifying the presence of homologous series and quantifying the number of their terms. A data pre-processing procedure is introduced to transform the time axis in order to display a strictly homogenous retention pattern: n-alkanes are used as external standard to stretch or shrink the original chromatogram in order to build up a linear GC retention scale. This addition can be regarded as a further step in the direction of a signal processing procedure for achieving a systematic characterization of complex mixture from experimental chromatograms. The EACVF_tot was computed on the linearized chromatogram: if the sample presents terms of homologous series, the EACVF_tot plot shows well-defined deterministic peaks at repeated constant interdistances. By comparison with standard references, the presence of such peaks is diagnostic for the presence of the ordered series, their position can be related to the chemical structure of the compounds, their height is the basis for estimating the number of terms in the series. The power of the procedure can be magnified by studying SIM chromatograms acquired at specific m/z values characteristic of the compounds of interest: the EACVF_tot on these selective signals makes it possible to confirm the results obtained from an unknown mixture and check their reliability.The procedure was validated on standard mixtures of known composition and applied to an unknown gas oil sample. In particular, the paper focuses on the study of two specific classes of compounds: n-alkanes and oxygen-containing compounds, since their identification provides information useful for characterizing the chemical composition of many samples of different origin. The robustness of the method was tested in experimental chromatograms obtained under unfavorable conditions: chromatograms acquired in non-optimal temperature program conditions and chromatographic data affected by signal noise.     

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.     

Prediction of retention indices. VI: Isothermal and temperature-programmed retention indices,methylene value,functionality constant,electronic and steric effects

The Kováts retention index system with n-alkanes as reference standards has properties not fully explored when single, isolated or stand-alone analytes are analyzed by isothermal gas chromatography. When a homologous series of analytes are analyzed by either linear or non-linear temperature-programmed gas chromatography, the retention data of the entire series can be treated systematically to produce an I vs. Z plot that is linear, thereby giving insight into the relationship between chemical structure and retention index. Dead time t_M is both instrument and temperature dependent. With no dead time t_M adjustment, the retention indices of analytes calculated from experimental retention times by the method of either linear or logarithmic interpolation give statistically identical values. Linear regression analysis of the data shows the slope as methylene value (A) and intercept as functionality constant or group retention factor (GRF) of the homologous series. The A and (GRF) values vary with chemical structures, intermolecular electronic and steric interactions, and polarity of column liquid phases, and can link gas chromatographic retention index to chemical structure. Examples of the influence of molecular electronic effects and steric effects on retention index are given and discussed.     

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.     

New five‐ring symmetrical bent‐core mesogens exhibiting the fascinating B7 phase

Three new homologous series of symmetrical five‐ring bent‐core compounds have been synthesized and investigated for their mesomorphic properties. The laterally unsubstituted parent compounds exhibit a metastable SmCP_A phase. However, the two series of compounds containing a strongly polar cyano or nitro group at the angular position of the central phenyl unit show the fascinating classical B₇ phase. The mesophases have been characterized using standard techniques.     

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.     

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.     

Synthesis and mesomorphic properties of a new chiral series with a heterocycle in the molecular core

We report a number of different homologous series with a heterocycle incorporated in the molecular core near the chiral chain. Two of these series differ in the type of chiral chain, -CH*(CH₃)C₆H₁₃ or -CH*(CH₃)-CO₂-C₄H₉. Their properties are compared and found to show completely different polymorphism. The first series exhibits only SmC* and SmA phases whereas the second possesses TGB, N* and BP phases. The mesomorphic properties were studied by optical microscopy, DSC and electro-optical measurements. The effect of substitution of the phenyl ring near the chiral chain by a heterocycle is discussed.     

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.     

Nuclear spin—lattice relaxation and molecular motions in the thermotropic mesophases of p-alkoxybenzylidene—p-n-alkylanilines

Experimental results of an investigation of the proton spin—lattice relaxation in a well-known homologous series exhibiting smectic polymorphism, are presented. Explanations for striking features of T₁ and T_1D dependences on temperature, frequency and molecular orientation in terms of molecular motions are proposed.     

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.     

On the Determination of the Hold-Up Time in Reversed Phase Liquid Chromatography

Abstract

The determination of the hold-up time in reversed phase liquid chromatography has been studied extensively for the mobile phase system methanol-water. Hold-up times obtained by static methods, linearization of homologous series and so-called “unretained compounds” are discussed and mutually compared. Several n-alkyldimethylsilyl bonded phases have been used for this investigation.

A rough estimate of the hold-up time can be obtained by using components of the mobile phase or highly concentrated salt solutions, but only for mobile phase compositions around 60% (v/v) methanol. Hold-up times accurate to 1% can be obtained over the complete range of mobile phase compositions from the linearization of net retention times of homologous series.     

Three ring dioxanes as dopants enhancing the stability of the smectic C phase

Abstract

Searching for compounds which could be useful as modifiers of smectic C mixtures, we have synthesized four homologous series of three ring dioxanes, 2BBD, 5BBD, 2CBD, and 5CBD. Their phase transition temperatures and enthalpies were measured and their liquid crystal phases identified. Compounds belonging to series n-BBD form smectic B_cr phases for shorter alkyl chains, and smectic B_cr and A phases, for longer chains. Compounds belonging to the n-CBD series exhibit the smectic A phase, but those with longer alkyl chains have exclusively smectic B phases and those with short tails have other low temperature, highly ordered smectic phases. The compounds were added to smectic C mixture and it was found that some can be useful as dopants. Compounds with longer alkyl tails in the molecule are more suitable for this purpose; the type of ring in the core is less important.     

Investigation of the Electronic Structure of Alkyl Allyl Radicals

The electronic structure of the homologous series of CH₃(CH₂)_nCHCHCH₂ (n = 0÷5) allyl all radicals is studied. The obtained spin density distribution is used to determine the fragment serving as the radical center. The delocalization of spin density over the basin of the radical center is shown to be responsible for two free valencies associated with two classical canonical structures (the conjugated fragment). The conjugation phenomenon is studied and electronic parameters are determined for the “standard” conjugated fragment CHCHCH₂.