Ethyl solvent polarity indicator

The diion mechanism c has been reported for at least some of the reae-tions in categories 3 and as well as some ketene dimerizations. For example, the rate of the reaction between l,2-bis(trifluoromethyl)-l,2-dicyanoe-thene and ethyl vinyl ether was strongly influenced by changes in solvent polarity.Some of these reactions are nonstereospecific, but others are stereo-specific. As previously indicated, it is likely that in the latter cases the di-ionic... 

Figure 18. Correlations between the solubility of cmchonidme and the reported empirical polarity (A) and dielectric constants (B) of 48 solvents [66]. Those solvents are indicated by the numbers in the figures 1 cyclohexane 2 n-pentane 3 n-hexane 4 triethylamine 5 carbon tetrachloride 6 carbon disulfide 7 toluene 8 benzene 9 ethyl ether 10 trichloroethylene 11 1,4-dioxane 12 chlorobenzene 13 tetrahydrofuran 14 ethyl acetate 15 chloroform 16 cyclohexanone 17 dichloromethane 18 ethyl formate 19 nitrobenzene 20 acetone 21 N,N-drmethyl formamide 22 dimethyl sulfoxide 23 acetonitrile 24 propylene carbonate 25 dioxane (90 wt%)-water 26 2-butanol 27 2-propanol 28 acetone (90 wt%)-water 29 1-butanol 30 dioxane (70 wt%)-water 31 ethyl lactate 32 acetic acid 33 ethanol 34 acetone (70 wt%)-water 35 dioxane (50 wt%)-water 36 N-methylformamide 37 acetone (50 wt%)-water 38 ethanol (50 wt%)-water 39 methanol 40 ethanol (40 wt%-water) 41 formamide 42 dioxane (30 wt%)-water 43 ethanol (30 wt%)-water 44 acetone (30 wt%)-water 45 methanol (50 wt%)-water 46 ethanol (20 wt%)-water 47 ethanol (10 wt%)-water 48 water. [Reproduced by permission of the American Chemical Society from Ma, Z. Zaera, F. J. Phys. Chem. B 2005, 109, 406-414.]...

The kinetic and activation parameters for the decomposition of dimethylphenylsilyl hydrotrioxide involve large negative activation entropies, a significant substituent effect on the decomposition in ethyl acetate, dependence of the decomposition rate on the solvent polarity (acetone-rfe > methyl acetate > dimethyl ether) and no measurable effect of the radical inhibitor on the rate of decomposition. These features indicate the importance of polar decomposition pathways. Some of the mechanistic possibilities involving solvated dimeric 71 and/or polymeric hydrogen-bonded forms of the hydrotrioxide are shown in Scheme 18. 

Solvent polarity parameters — use solvatochromic dyes (dyes whose electronic transitions are strongly dependent on the nature of the solvent) as indicators of solvent polarity. A comprehensive solvent polarity scale was first proposed by Kosower who defined the polarity parameter, Z, as the molar transition energy, Ej, for the charge transfer band of 1-ethyl-(methoxycarbonyl)pyridynium iodide in a given solvent as... 

Combination and disproportionation are, of course, preceded by the occurrence of a different transition complex. It seems that the transition complex leading to the disproportionation of small radicals (ethyl) is more compact than that from which the combined complex is generated. Nevertheless, they both have a loosened structure. The mechanism of disproportionation is not known in detail. The high A factor indicates that a simple abstraction of the / hydrogen by one radical from the other is not probable. The transition complex may be polar [2] a direct proof is not accessible. The rate is determined by diffusion [3] the effect of solvent polarity on the activation parameters cannot be measured. The value of fct (comprising combination and disproportionation) of two small radicals is of the order of 109 mol-1 dm3 s l at temperatures around 273 K. 

Ionic contributions to the transition state are also indicated from the effect of solvent polarity upon the rate of decomposition of l,2-di- -propyl-l-carbo-I-butylperoxycyclopropene. A linear correlation is observed with the yvalues of Dimroth and Reichardt for the following solvents ethyl benzene, chlorobenzene, benzonitrile, acetonitrile and benzyl alcohol . 

Z polarity scale. A solvent polarity scale proposed by Koso ver [Kosower 1958a, 1958b] based on the energy of the electronic transition of the 1 -ethyl-4-carbomethoxypyridinium iodide that is strongly solvent-dependent. This is a measure of an internal charge transfer process. The original set of Z values being quite small, it was successively extended by means of other indicators (Table L2). 

The incorporation of lipid-heme in the liposome was studied by fluorescence spectral measurement using porphinatozinc as the fluorescent probe For homogeneous alcohol solutions of the porphyrinatozinc, the fluorescence intensity increased with the decrease of the solvent polarity (methyl, ethyl, and butyl alcohol), as expected. The intensity was much larger, more than twice, for the liposome-embedded porphinatozinc than those in alcohols, indicating that the porphinatozinc is incorporated into the hydrophobic region of the lipid bilayer and is molecularly dispersed in the liposome. This supports also the incorporation of the heme in the liposome. 

Molecular orbital calculations have been carried out on 2-fluoro- and 2-chloro-tetrahydropyrans as models for examining the anomeric effect in gtycosyl halides. The calculated population of the axial conformer decreased as the solvent polarity increased, which indicated a consequent decrease in the anomeric effect.The synthesis of a series of 2-(perfluoroall yl) ethyl glycosides is mentioned in Chapter 3, and some 3 -fluorinated ribonucleosides are covered in Chapter 20. The syntheses of 2-fluoro-L-daunosaniine and 2-fluoro-D-ristosamine are discussed in Chapter 9, while 2 -fluorocarminontydn is described in Chapter 19, and some fluorinated 2-deoxy KDO analogues are covered in Chapter 16. 

Initially, a reaction of A-acetoxy-A-butoxybenzamide 25c with A-methyl aniline 61 in butyl benzoate 63(R = Bu) and acetic acid. Close examination of these highly coloured reaction mixtures indicated the presence of crystals of A,A-dimethyl-A,A-diphenyltetrazene 65 (Scheme 11, R = Bu). The reaction is promoted by polar solvents as reactants are unchanged in pure acetonitrile. A crossover experiment using a mixture of /V- a ce t o x y - A-- b u t o x y - to 1 u a m i d e 26d and A-acetoxy-A-ethoxybenz-amide 25a afforded clean yields of butyl /Moluatc and ethyl benzoate thus pointing to an intramolecular rearrangement.41... 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

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