Substituent Alkyl Chain Length

The incorporation of alkyl substituents of increasing chain length in a non-symmetrical arrangement on the ions leads to the introduction of bulk into the crystalline lattice that disrupts the attractive charge-charge lattice. Relatively short 

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Figure 29. For the latter case, it is considered that the semiconducting re-electron systems are separated by insulating hydrocarbon spacers, resulting in alternate thin layers of organic semiconductor and insulator in these monolayer assemblies. The direct current - voltage (I - V) characteristics were mea- sured for the multilayers H2Pc(R)8 and Cu-Pc(R)8 in directions perpendicular and parallel to the film plane. In both cases, the linear I - V relationships of Ohm s law were observed at low electric field and obtained DC conductivities are summarized in Table 3. The normal conductivity (ajJ were ca. 10 13 S cm-1, while the lateral ones p//) were 3.4 x 10-7 and 9.9 x 10 7 S cm 1 for films of the metal-free and copper Pc derivatives, respectively. The former (ojJ tended to decrease slightly with increase of Figure 29. Schematical illustration of the substituent alkyl chain length,...

In addition, the steric bulk of several substituents on an amino group appears to disturb the structure of the membrane more than a single substituent. Amw for a series of (/>-mcthylbcnzyl)alkylamincs increase with increasing alkyl chain length [153]. This trend was not observed for the corresponding octanol-water partition data, which is additional evidence that the increase in Amw is caused by an unfavourable steric constraint. The positively charged... 

A wide variety of physical properties are important in the evaluation of ionic liquids (ILs) for potential use in industrial processes. These include pure component properties such as density, isothermal compressibility, volume expansivity, viscosity, heat capacity, and thermal conductivity. However, a wide variety of mixture properties are also important, the most vital of these being the phase behavior of ionic liquids with other compounds. Knowledge of the phase behavior of ionic liquids with gases, liquids, and solids is necessary to assess the feasibility of their use for reactions, separations, and materials processing. Even from the limited data currently available, it is clear that the cation, the substituents on the cation, and the anion can be chosen to enhance or suppress the solubihty of ionic liquids in other compounds and the solubihty of other compounds in the ionic Hquids. For instance, an increase in alkyl chain length decreases the mutual solubihty with water, but some anions ([BF4] , for example) can increase mutual solubility with water (compared to [PF JT for instance) [1-3], While many mixture properties and many types of phase behavior are important, we focus here on the solubihty of gases in room temperature ILs. 

Similar to the imidazolium ILs, very low solubility of the ammonium ILs was observed in alkanes. Eor example, the solubility of butyl(2-hydroxyethyl) dimethylammonium bromide, [(Ci)2C4HOC2N]Br, exhibited a simple eutectic system with immiscibility in the liquid phase in the IL mole fraction range from XjL = 0.02 to 0.70 [53] the other ammonium salt, (benzyl)dimethyl-alkylammonium nitrate, [Be(Ci)2C N] [NOJ showed very small solubility in the liquid phase in hexadecane and it was slightly better in hexane (immiscibility from XjL = 10 to 0.90) [99] for the ammonium salt with an alkane substituent only, didecyldimethylammonium nitrate, [(Cio)2(Q)2N][N03], the solubility in the liquid phase was better in hexane (immiscibility from XjL = 10 to 0.50) than in hexadecane, where the immiscibility was observed in the whole IL mole frachon [100]. In all systems with imidazolium and ammonium salts, an increase in the alkyl chain length of the alkane (solvent) resulted in a decrease of solubility. 

Why is it necessary to increase the proportion of acetonitrile in the mobile phase as the alkyl chain-length of the C5 substituents increases ... 

Materials that are solubilized in polyethylene glycol can be solubilized in the polyoxyethylene chains on the surface of a nonionic micelle. Ismail, Gouda, and Motawi found that the micellar partition coefficients of barbiturates in polysorbates 20, 40, 60, and 80 is a function of the solute substituents and is proportional to the octanol-water partition coefficient of the barbiturate. Similarly, Ikeda, Kato, and Tukamoto showed that the solubilization of alkyl barbiturates by polyoxyethylene lauryl ether is not dependent upon the number of carbons in the substituents. Since the different polysorbates contain different aliphatic groups, the rather small dependence of solubilization upon polysorbate number (i.e., upon alkyl chain length) suggests that the barbiturates are not solubilized primarily in the hydrocarbon portion of the micelle. Gouda, Ismail, and Motawi showed that the solubilization of barbiturates in polyoxyethylene stearates is proportional to the number of polyoxyethylene units in the surfactant. 

Lin et al. have studied variations in the chemical shifts for a variety of methyl-imidazolium salts with different alkyl chain substituents and Br, BF , and BF" anions [8]. They observed a high sensitivity in chemical shift (depending, among other factors, predominantly on the alkyl chain length) for the 2-proton in the imidazolium ring. The effect was most pronounced for the bromide salts. Additionally, they observed unexpected H/D exchange for the 2-proton. Today, these results can be interpreted as H-bonding effects, and of course the acidity of H2 comes to no surprise ([3,9] and references therein). 

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