Melting behaviour of a series of diamides

The melting behaviour of diamides of general formula (n — C_pH_2p+1)CONH-(CH₂)_qNHCO(n — C_pH_2p+1) has been investigated by calorimetric, dilatometric and IR techniques. The conformational contribution to the melting entropy, calculated from the hypothesis of complete conformational freedom of the molecules at the melting point, has been compared with the experimental data. The higher melting points of the diamides, as compared with those of the linear hydrocarbons having the same number of conformationally flexible chain bonds, are attributed to a reduction of conformational freedom of the chain segments in the liquid state (caused by the large fraction of hydrogen bonds maintained in the melt).     

Melting behaviour of a series of monoamides

The melting behaviour of the monoamides of general formula (n-C_pH_2p+1)CONH-(n-C_qH_2p+1) is investigated by differential scanning calorimetry (DSC) and infrared spectroscopy. The lower values of melting entropies, compared to those for linear hydrocarbons with the same number of conformationally flexible chain bonds, is attributed to a reduction in the number of conformations available to the hydrocarbon portion of the molecule, because of the large amount of hydrogen bonding maintained in the melt. The melting behaviour of the monoamides is compared with that of the diamides discussed in a previous paper [1]. The persistence of a network of hydrogen bonds in the melt of the diamides reduces the conformational freedom of the chain segments more than for the monoamides.     

新的混合柔链苯并菲盘状液晶：分子对称性与宽温柱状介晶相

A series of new trialkoxytrialkanoyloxytriphenylene TP（OCnH2n＋1）3（OCOCmH2m＋1）3 （5a-5e） （n =m＋1 =4- 8） discotic liquid crystals were prepared and their mesomorphic properties were investigated using differential scanning calorimetry （DSC） and polarizing optical microscopy （POM）. The symmetrical and shorter chain triphenylenes display higher melting points and clearing points, more highly ordered and stable columnar mesophase than the asymmetrical and longer chain triphenylenes respectively.     

Synthesis of unsymmetric triphenylene discotic liquid crystals with a semi-fluorinated chain and the influence of fluorophobic effect on mesogenic behavior

The fluorophobic effect of the semi-fluorinated chain of discotic molecules efficiently improves the stability of columnar mesophase.Low symmetric discogens exhibit decreased melting points and wide mesophase ranges.A series of triphenylene derivatives 1,C18H6(OCnH2n+1)4(OMe)(O2CC2H4C6F13),and their hydrocarbon analogues 2,C18H6(OCnH2n+1)4(OMe)(O2CC8H17),n = 4―8,were synthesized for the investigation of the influence of semi-fluorinated peripheral chain and molecular symmetry on mesomorphism.The structures ...     

Collision spectroscopy with aligned and oriented atoms

Electron capture processes in the H⁺?Na(3s) and H⁺?Na(3p) collisions are experimentally investigated in the 0.3–3 keV energy range using a crossed beam experiment. The excited Na(3p) target is produced with a well-defined alignment using laser pumping. The time of flight technique enables the identification of all the H(n)+Na⁺ channels populated in the collision. Total cross section ratios σ_3p (n=2)/σ_3s (n=2),σ_3p (n=3)/σ_3s (n=2) and σ_3s (n=3)/σ_3s (n=2) for the production of H(n=2) and H(n=3) are measured in the H⁺?Na (3s) and H⁺?Na (3p) collisions. They reveal a strong dominance of the production of H(n=2) in the H⁺?Na(3p) collision, especially for energies below 1 keV.     

Substituent effects on the kinetics of the cerium(IV) oxidation of mandelic acids in sulfate media. Anomalous kinetic behavior of the methoxy derivative

The kinetics of the cerium(IV) oxidation of p-nitro and p-methoxymandelic acids have been investigated in H₂SO₄-MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) and H₂SO₄-MClO₄ (M⁺ = H⁺, Na⁺) mixtures at a constant total electrolyte concentration of 2.00 mol/dm³. The oxidation of p+nitromandelic acid proceeds through two [H⁺]-independent paths, as was also observed for some substituted mandelic acids studied previously. The kinetic behavior of the p-methoxy derivative differs from that of the other mandelic acids in that (1) the oxidation occurs via two [H⁺]-dependent paths, (2) the reaction rate is anomalously high, (3) the activation enthalpy and entropy of the overall process are markedly lower. It provides strong support to the suggestion that a different mechanism is operative. The substituent effects and the reaction mechanism are discussed.     

Thermodynamics of phase transitions and heat capacities of monosubstituted n-alkanaminium bromides above room temperature

Differential scanning calorimetry was applied to examine the thermodynamics of solidstate phase transitions and fusion processes of compounds of the general formula (n-C_pH_2p+₁NH₃)Br (wherep=0–3). The heat capacities of the compounds in the range from ambient temperature to the onset of their volatilization were also studied. All the thermochemical characteristics reveal a dependence on the structure of the alkanaminium cations.

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Zusammenfassung Unter Anwendung von DSC wurde die Thermodynamik von Feststoff-Phasenübergängen und Schmelzvorgängen bei Verbindungen der allgemeinen Formel (n-C_pH_2p+₁NH₃)Br (mitp=0–3) untersucht. Weiterhin wurde die Wärmekapazität der Verbindungen im Temperaturbereich Raumtemperatur bis Einsatz der Verdampfung untersucht. Alle thermochemischen Eigenschaften lassen eine Abhängigkeit von der Struktur des Alkanaminium-Kations erkennen.

     

Formation of H3O+ from alcohols and ethers induced by intense laser fields

The processes of H₃O⁺ production from alcohols (ethanol, 2‐propanol, 1‐propanol, 2‐butanol) and ethers (diethyl ether and ethyl methyl ether), and their deuterium‐substituted species, by intense laser fields (800 nm, 100 fs, ～1 × 10¹⁴ W/cm) were investigated through time‐of‐flight (TOF) mass spectrometry. H₃O⁺ formation was observed for all these compounds except for ethyl methyl ether. From the analysis of TOF signals of H_(3?n)D_nO⁺ (n = 0, 1, 2, and 3) that have expanding tails with increasing flight time, it has been confirmed that the reaction proceeds through metastable dissociation from the intermediate species C₂H_(5?m)D_mO⁺(m = 0–5). The common shape of the H_(3?n)D_nO⁺ signal profiles contains two major distributions in the time constant, i.e., fast and slow components of <50 ns and ～500 ns, respectively. The H_(3?n)D_nO⁺ branching ratio is interpreted to be the result of complete scrambling of four hydrogen atoms at the C? C site in C₂H₄‐OH⁺, and partial exchange (18–38%) of a hydrogen atom in the OH group with four other hydrogen atoms within 1 ns prior to H_(3?n)D_nO⁺ production. Ab initio calculations for the isomers and transition states of C₂H₅O⁺ were also performed, and the observed H_(3?n)D_nO⁺ production mechanism has been discussed. In addition, a stable isomer having a complex structure and two isomerization pathways were discovered to contribute to the H₃O⁺ formation process. Copyright © 2010 John Wiley & Sons, Ltd.     

Photochromism and decolorization controlled by auxiliary ligands of complexes derived from 1‐methyl‐4,4′‐bipyridinium cation

Three 1‐methyl‐4,4′‐bipyridinium (MQ⁺)‐based complexes, {[Cd(MQ)(p‐BDC)Br]?H₂O}_n ( 1 ), {[Cd(MQ)(m‐BDC)(H₂O)Br]?3H₂O}_n ( 2 ) and Cu(MQ)Br₂ ( 3 ) (p‐H₂BDC = 1,4‐benzenedicarboxylic acid, m‐H₂BDC = 1,3‐benzenedicarboxylic acid), have been synthesized and structurally characterized. Compounds 1 and 2 are one‐dimensional coordination polymers constituted of one coordinated MQ⁺ cation, one coordinated Br^? ion and chains of Cd²⁺ ions connected by deprotonated BDC^2? units, which both have photochromism but different decolorization behaviors. The structures and photoresponsive behaviors controlled by auxiliary ligands have been explored. Compound 3 is constituted of one Cu⁺ center, one MQ⁺ ligand and two coordinated Br^? ions in a ‘V’ configuration, exhibiting no photochromism.     

Striking differences between alkyl sulfate and alkyl sulfonate when mixed with cationic surfactants

The properties of alkyl sulfate and alkyl sulfonate are similar except for their Krafft points. However, alkyl sulfate and alkyl sulfonate behave quite differently when they are mixed with cationic surfactants and show some totally unexpected results. In this work sodium alkyl sulfate (C_nH_2n+1SO₄Na,C_nSO₄)–alkyl quaternary ammonium bromide [C_nH_2n+1N(C_mH_2m+1)₃Br, C_nN, m=1–4] mixtures and sodium alkyl sulfonate (C_nH_2n+1SO₃Na, C_nSO₃)–C_nN mixtures were studied. It was found that, in contrast to the single surfactants, C_nSO₃–C_nN mixtures were much more soluble than C_nSO₄–C_nN mixtures. Besides, the two kinds of catanionic surfactant mixtures were quite different in their phase behavior and aggregate properties. The results were interpreted in terms of the interactions between surfactant molecules, which were very different in the two kinds of mixed systems owing to the distinction between alkyl sulfate and alkyl sulfonate in the molecular charge distribution.     

Quantum-chemical simulation of boron- and halogen-containing polymers

Quantum-chemical method of density functional theory B3LYP/6-311+G(d,p) was used to study the energy and structural characteristics of boron- and halogen-containing condensation polymers C _n+2H _n+4B_2n X _n (X = F, Cl, Br; n = 1, 2, …), constructed based on 1,2,6-halodiborenes. All possible condensation versions were analyzed and the structure of the most stable polymer was established. It was shown by AIM-analysis that in the systems under consideration bicoordinated halogen atoms were present.     

Reaction of ammonia with accelerated benzoyl ions under multiple-collison conditions in a triple quadrupole instrument

The reaction of benzoyl ion with ammonia in multiple-collision conditions in the second quadrupole assembly of a triple quadrupole mass spectrometer at (laboratory) ion kinetic energies from 0 to 20 eV produced the even-electron ions [C₆H₅]⁺, [C₆H₅NH₃·(NH₃)_m]⁺ (m = 0, 1) and [C₆H₅CONH₃·(NH₃)_n]⁺ (n = 0, 1, 2, 3) and the odd-electron ions [C₆H₄NH₃·(NH₃)_p]⁺· (p = 0, 1). Thermochemical information could not be obtained under multiple-collision conditions: both exothermic and endothermic reactions were observed, with no translational-energy onset measurable for the endothermic processes, nor decrease in the yield of the exothermic processes at high energies. The behaviour of cluster-ion intensities as pressure varied was qualitatively as expected. There are pressure and energy regions where spectra change little; if this feature were to be general, it would point to some utility for these conditions in qualitative analysis.     

Transfer Hydrogenation of Ketones Catalyzed by Surface‐Active Ruthenium and Rhodium Complexes in Water

An improved, high‐yield, one‐pot synthetic procedure for water‐soluble ligands functionalized with trialkyl ammonium side groups H₂N(CH₂)₂NHSO₂‐p‐C₆H₄CH₂[NMe₂(C_nH_2n+1)]⁺ ( [HL ⁿ ]⁺ ; n=8, 16) was developed. The corresponding new surface‐active complexes [(p‐cymene)RuCl( L ⁿ )] and [Cp*RhCl( L ⁿ )] (Cp*=η⁵‐C₅Me₅) were prepared and characterized. For n=16 micelles are formed in water at concentrations as low as 0.6 mM , as demonstrated by surface‐tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C₁₆ tails due to their ability to be adsorbed at the water/substrate interface. The scope of these catalyst systems in aqueous solutions was extended from partially water soluble aryl alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (2‐dodecanone).     

Effect of method of ion preparation on low-energy collision-induced dissociation mass spectra

The collision-induced dissociation (CID) mass spectra of protonated cocaine and protonated heroin have been measured using a triple quadrupole mass spectrometer at 50 eV ion/neutral collision energy for protonated molecules prepared by different protonating agents. The CID mass spectra of protonated cocaine using H⁺(H₂O)_n, H⁺(NH₃)_n and H⁺((CH₃)₂NH)_n as protonating agents are essentially identical and it is concluded that, regardless of the initial site of protonation, the fragmentation reactions occurring on collisional activation are identical. By contrast, protonated heorin prepared with H⁺(H₂O)_n and H⁺(NH₃)_n as protonating agents show substantial differences. That formed by reaction of H⁺(H₂O)_n shows a much more abundant peak corresponding to loss of CH₃CO₂H. From a comparison with model compounds, and from a consideration of the three-dimensional structure of heroin, it is concluded that with H⁺(H₂O)_n as protonating agent significant protonation occurs at the acetate group attached to the alicyclic ring, leading to acetic acid loss on collisional activation, but that reaction of H⁺(NH₃)_n leads to protonation at the nitrogen function. The proton attached to nitrogen cannot interact with the acetate group and, consequently, the probability of loss of acetic acid on collislional activation is greatly reduced.     

Interaction of the Benzenium Ion with Inert Ligands: IR Spectra of C6H7+?Ln Cluster Cations (L=Ar,N2, CH4, H2O)

IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C₆H₇⁺) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C₆H₇⁺? Ar, C₆H₇⁺? (N₂)_n (n=1–4), C₆H₇⁺? (CH₄)_n (n=1–4), and C₆H₇⁺? H₂O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm^?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C₆H₇⁺. The C₆H₇⁺? (CH₄)_n clusters show additional C? H stretch bands of the CH₄ ligands. Both the frequencies and the relative intensities of the C₆H₇⁺ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C₆H₇⁺? L_n clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm^?1 (≈9.5 and 11.5 kJ mol^?1) for N₂ and CH₄, respectively. The interpretation of the experimental data is supported by ab initio calculations for C₆H₇⁺? Ar and C₆H₇⁺? N₂ at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N₂ to the C₆H₇⁺ ring. The astrophysical implications of the deduced IR spectrum of C₆H₇⁺ are briefly discussed.     

Preparation and properties of surface-active organocobalt complexes having long-chain alkyl groups

New types of surface-active organocobaltocenium(I) complexes, η-C_nH_2n+1X-C₅H₄(ηC₅H₅)₂Co⁺Y^? and(η-C_nH_2n+1X-C₅H₄)Co⁺Y^? (n = 6–16; X not present, NHCO or OCO; Y = Cl or PF₆) were prepared and their surface character studied. (1) The critical micelle concentrations of the cobaltocenium chlorides were much lower than those of corresponding trimethylammonium-type cationic surfactants. (2) The surface-active character of the cobaltocenium chlorides in aqueous solution (and the redox potentials of the hexafluorophosphates in acetonitrile) were affected by the substituents (X) in the cyclopentadienyl groups. (3) The surface activities of the cobaltocenium salts were lost on reduction with NaBH₄ to afford (alkyl-substituted cyclopentadiene) cyclopentadienylcobalt (0) complexes which were surface-inactive but could be re-oxidized to afford the surface-active cobaltoceium(I) salts. The cobalt complexes mentioned above may be the first examples of redoxresponsive surfactants.     

Luminescent sensing of Fe3+ and K+ by three novel imidazole dicarboxylate-based MOFs

In this paper, three luminescent metal–organic frameworks, namely: [Zn(p-IPhHIDC)]_n (1), {[Cd(p-IPhIDC)(H₂O)]·CH₃OH}_n (2) and [Zn(p-TIPhHIDC)]_n (3), bearing two novel substituted imidazole dicarboxylate ligands, 2-(p-N-imidazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic acid (p-IPhH₃IDC) and 2-p-(1H-1,2,4-triazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic acid (p-TIPhH₃IDC), have been prepared and characterised through infrared spectra, X-ray powder diffraction, elemental analyses, thermogravimetric analyses and single-crystal X-ray diffraction. Ignoring the free methanol molecule and coordinated water in 2, 1–3 are similar structures. Moreover, the luminescent properties of the MOFs have been explored. It was found that MOFs 1 and 2 show good luminescent sensing of Fe³⁺ in varying degrees, and 3 of K⁺.     

Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions

Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C₂H₄)_n(CH₃OH)_mH⁺]/[(C₂H₄)_n(CH₃OH)_m⁺], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C₂H₄)_n(CH₃OH)_m⁺ and (C₂H₄)_n(CH₃OH)_m–1CH₃O⁺ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C₂H₄)_n(CH₃OH)_mH⁺ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH₃OH)H₃O⁺, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C₂H₄)_n(CH₃OH)_mH⁺(n + m ≤ 3) using semi-empirical molecular orbital calculations.     

Mesogens based on palladium orthometallated complexes with carboxylato bridges: tuning and shaping a non-planar molecule

The binuclear cyclopalladated compounds [Pd₂(μ-OH)₂(Lⁿ)₂] (1) derived from imines HLⁿ = p-C_nH_2n + 1O-C₆H₄-CHN-C₆H₄-OC_nH_2n + 1-p (n = 6,10) react with carboxylic acids to give the derivatives [Pd₂(μ-ox)₂(Lⁿ)₂] (2) with a planar core for oxalic acid, and [Pd₂(μ-OOCR)₂(Lⁿ)₂] (3-7) compounds with a non-planar ridge tent structure for other RCOOH acids: (3) R = C_mH_2m + 1 (m = 1, 3, 5, 7, 9, 11, 13, 15, 17); (4) R = CH₂(OCH₂CH₂)_pOCH₃ (p = 1, 2); (5) R = CH₂-C₆H₄-OC_qH_2q + 1-p (q = 2, 4, 6, 8, 10, 12); (6) R = C₆H₄-OC_rH_2r + 1-p (r = 4, 10); (7) R = C*H(OH)CH₃. The acids used were designed to explore the effect on the thermal properties of the compounds prepared of systematic variations in the type of carboxylato ligand, which induce structure, packing, and polarity changes, and in the length of the carboxylato chain. Most of the complexes prepared, even when far from planar, show liquid crystal behavior and display nematic, smectic A and smectic C phases.