Unpolar solvents

The absorption spectrum of TIN in methylcyclo-hexane/isopentane at 150 K is represented by curve I, Fig. k. Curve III shows the absorption spectrum of MT in hexane at 296 K. In unpolar solvents the intra-molecular hydrogen bond of TIN is still intact (curve... 

II). From this it must be concluded that the long-wavelength absorption of curve I is due to the intra-molecular hydrogen bond of TIN in unpolar solvents as the intensity of this band is reduced in polar solvents (curve II) and disappears completely in the spectrum of MT (without intramolecular hydrogen bond), curve III. Curve IVa represents the fluorescence and IVb the phosphorescence emission of both TIN and MT in... 

The micelle formation is not restricted to solvents for polystyrene but also occurs in very unpolar solvents, where the fluorinated block is expected to dissolve. Comparing the data, we have to consider that the micelle structure is inverted in these cases, i.e., the unpolar polystyrene chain in the core and the very unpolar fluorinated block forming the corona. The micelle size distribution is in the range we regard as typical for block copolymer micelles in the superstrong segregation limit.2,5,6 The size and polydispersity of some of these micelles, measured by DLS, are summarized in Table 10.3. 

Table 10.4 summarizes the compositions of some experiments as well as the colloid-analytical data of the final polystyrene lattices. A particle diameter of about lOOnm (including the shell of the adsorbed block copolymers in an extended conformation) is rather low for the product of a dispersion polymerization in unpolar solvents. In addition, a mean deviation (a) of about 20% of the particle size indicates a well-controlled and stable latex. 

Solvents exert control on the chemose-lective hydrogenation of alkenes bearing a benzyloxy protecting group [160]. In the unpolar solvent benzene, only the double bond is hydrogenated, while in methanol, acetone, and ethyl acetate, the benzyloxy group is also removed. Selective... 

Optically active benzene(poly)carboxamides and benzene(poly)carboxy-lates were used by Inoue and co-workers as sensitizers for the geometrical photoisomerization of (Z)-cyclooctene and (Z,Z)-cyclooctadienes in various solvents at different temperatures. Under energy-transfer conditions, enantiomeric excesses up to 64% ee in unpolar solvents like pentane were reported. The use of polar solvents diminished the product ee s due to the intervention of a free or solvent-separated radical ion pair generated through the electron transfer from the substrate to the excited chiral sensitizer (Scheme 58) [105-109]. 

The unpolar solvent required rather long reaction times, but allowed one to identify a Rh(I) intermediate, [Rh(CO)2]2(OEP), which carries two Rh(CO)2 groups on both sides on the porphyrin ring and is a typical example of a bimetallic porphyrin [8]. A photochemical variant of this insertion in benzene/tetrachloromethane [58] accelerates the reaction and gives a 50% yield of RhCl(OEP)H20. Aoyama, Ogoshi et al. [59] used [RhCl(CO)2]2 and carefully purified benzene. The solution of the porphyrin with the metal carrier was... 

Berman et al. have determined the conformation of chromomycin A3 by H-NMR spectroscopy in an unpolar solvent [227]. The conformation was determined via interresiude NOEs, which showed that there are contacts between the ends of the oligosaccharide chains, thus requesting a conformation with both chains bent to each other while the aromatic system is exposed. The mechanism of the interaction of this antibiotic with DNA was shown in a preliminary study to be consistent with an intercalation process [228], A note added in proof states that NOEs are not in agreement with an intercalation procedure. 

The conformation is proved by a significant NOE between the aldimine proton and the anomeric proton [17,24]. In polar solvents, free cyanide attacks the complex A, preferably from the unshielded Si-side. In unpolar solvents like chloroform, cyanide is not set free from the silyl derivative. The activation of the cyanide proceeds by an interaction between the exo chloride of the zinc complex and the silyl group. Thus, the cyanide is directed to the Re-side of the glycosyl imine (see Scheme 8). This nucleophilic attack produces L-aminonitriles with moderate or good stereoselectivity (S R 3-9 1) and high yields. 

The stereoelectronic effect of the RO-group is less pronounced, when bulkier electrophiles are employed (Table 3, entries 23,27,28), but is increased when the well solvating agent hexamethyl phosphorous amide (HMPA) is used as an additive 61,68). On the other hand, if one performs the deprotonation/alkylation sequence in the unpolar solvent pentane, a complete reversal of the stereochemical outcome provides the coproduct in excess (Eq. 35)61 Now a coordination of the lithium cation to the siloxy function might favour structures like 109 (or its oligomers) and cause predominant formation of cO-cyclopropanes. 

The formation of t-butylphosphaketene starts shortly above — 90°C, whereby the phospha analog of the carbamide acid chloride can be detected as an intermediate by 31P NMR. Above — 60°C its dimerization to the diphosphetandione [Eq. (74)] takes place this molecule is only reasonably stable at room temperature in unpolar solvents such as pentane. Adding polar agents or exposure to light causes decomposition. One of the products is triphosphetanone, which was synthesized before (102, 140). Even the better characterized tri-i-butylphenyl-substituted phosphaketene shows a slow decomposition in toluene, when irradiated by a mercury lamp over a period of 24 hr, splitting off CO. Some of the 31P NMR spectroscopically identified products are dihydro-phosphaindole, phosphane, and diphosphene (Scheme 18). Attempts to detect the expected phosphinidene intermediate failed. The decomposition mechanism itself is still unclear (117, p. 24). 

Table 2. Phenols and oxidation products from the reaction of pyrylium salts and nitromethane with 1 mole NR3 in unpolar solvents... 

It is less polar than chloramine and has a higher solubility in unpolar solvents. Solutions containing NH4+ are relatively stable at pH = 3.5-4 with about 10% decomposition per day, whereas solutions without NH4+ ions decompose totally within hours. The ammonium ions inhibit the decomposition by reacting with hypochloric acid HOCl, which is formed in small amounts by the hydrolysis of NHCI2 and accelerates the decomposition of dichloramine. 

As may be expected from their zwitterionic nature, the A, 5/-silicates la-7a and the X Ge-germanates lb-7b are high-melting crystalline solids All compounds are almost insoluble in unpolar solvents and exhibit very poor solubility in polar organic solvents. 

For the first reduction the IR shifts point to a porphyrin-centred electron transfer. This is supported by further spectroscopy on the anion radical complexes [(Por)Ru(CO)(L)]. The observed EPR lines are narrow, unstructured, with g values around 2. The UV-Vis-NIR spectra of the radical anions are characterised by redshifted Soret bands of reduced intensity, a weak structured band system around 600 nm and weak broad absorptions around 800 or 900 nm (see Figure 4.15). Further support comes from resonance Raman investigations on [(OEP)Ru(CO)(THF)] for which the observed Raman bands fit perfectly to those of the [(OEP)VO] radical anion. There is some evidence that if the spectroelectrochemistry is not carried out in very aprotic and unpolar solvents or traces of water are present, the radical anionic complexes are readily transformed. This has been investigated for the [(OEP)Ru(CO)(L)] system, where the use of solvents like MeOH or nitriles for the electrochemical reduction leads to altered species with unreduced porphyrin ligands (see Figure 4.15)." ... 

If large quantities are used for technical processes, e.g. for cleaning, the recovery and reuse of the microemulsion or at least of a considerable amount of the most expensive components is desired. Therefore, strategies are needed to separate contaminants from the organic microemulsion components. Separation is usually more complicated than from ordinary solvents and often requires several steps [39, 40]. In particular, the separation of waste materials from the surfactants is usually very difficult or often even impossible. The temperature-dependent phase behaviour of bicontinuous microemulsions, however, can sometimes be beneficially used for separation [41]. Easy separation, at least from the unpolar solvent, can be achieved from microemulsions with supercritical liquids [42]. 

Many pesticide residues are lipophilic, and a solvent not miscible with water may be used. Residues that have very low water solubility could be extracted with very unpolar solvents, like pentane, from samples that have been pulverized together with water-free sodium sulfate that take up the water. 

Whereas the insertion of ynamines into a metal-alkynylcarbene bond to give 18 is initiated by a nucleophilic attack at the carbene carbon atom, [21] the less nucleophilic ( softer ) 3-acyl enamine 19 rather adds to the ( softer ) P-carbon of the alkynylcarbene ligand to give l-metala-l,3,5-hexatriene 20 which upon thermolysis in unpolar solvents undergoes cyclization and demetala-tion to homopyrrole 21 (Scheme 11). [22]... 

Ofloxacin is by far the most representative of the N-l/C-8 tricyclic derivatives only a few other quinobenzothiazine derivatives [41] or pyridobenzothia-zine isosteres of ofloxacin derivatives [40] have been reported. Figure 18 shows the preparation of 7-oxo-2,3-dihydro-7H-pyrido(l,2,3-de) (1,4)benzothiazine-6-carboxylic acids. Interestingly, chlorine substitution of derivative 22 occurred in polar or unpolar solvents only after enhancement of the aromatic nucleus reactivity by oxidation of thiazinic sulfur to sulfoxide or sulfone 23 and 24. Derivative 25 substituted with IV-methylpiperazine (MF-934) was found slightly less active in vitro but more toxic than ofloxacin [40]. 

A variety of 3-D superlattices formed from metal nanopartides has been reported [1-8]. For instance, gold nanopartides, when stabilized by alkylthiolates RS (R = n-Ci2H2s) and rather narrowly distributed in size, could be obtained by the repeated fractional crystallization of a mixture of 1.5-3.5 nm particles from unpolar solvents. The success of fractionation was controlled by mass spectroscopy [6j. Based on these data, definite numbers of atoms could be assigned to the particles of distinct fractions (e.g., 140, 225, 314, and 459), all of which consisted of fee-structured octahedra. Solutions of these remarkably well-defined particles can be used to... 

Still, the electrostatic interactions are especially important in polar solvents because in these solvents, charges dissociate more easily than in unpolar solvents. 

Whereas the cycloisomerization of allenic ketones affords achiral products, replacing the keto with a hydroxy group leads to the formation of chiral heterocycles. In 2001, the synthesis of chiral 2,5-dihydrofurans by treatment of a-hydroxyallenes with catalytic amounts of AuCls in unpolar solvents was reported (Scheme 4-90). Many functionalities (e.g., carbonyl groups, additional free alcohols, and acid-sensitive... 

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