Ethanol solvent effects

The surfactant effects of 10% SLS on the system eoeffidents of the P/W system are shown in Figure 5.3. The changes in system coeffieients represent [Ac, Ar, As, Aa, Ab, AvJlio Note that the effects of the SLS surfaetant on the system coeffidents were similar to the ethanol solvent effects. The system eoeffieients were altered by... 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

The data in Table 2 show that with CD concentration around of 10 4 M, the addition of ATA resulted in slight increase in the reaction rate, but a decrease in the ee24o values was observed, with eemax unchanged. By adding ATA, at [CD] = 10 5 M, beside increased activity shown by ki ami k2 about 25 % increase of ee value was observed. Different from the observation in the hydrogenation of Etpy, this ATA effect was observed in ethanol solvent. This may be explained as... 

When we perform experiment in such way that there is no interference of H-bonds or these bonds are stable and structure of solvent also does not varies essentially, solvatochromic plot demonstrates very good linearity as shown, for example, for some naphthylamine derivatives in ethanol-water mixtures. The linearity of solvatochromic plots is often regarded as an evidence for the dominant importance of nonspecific universal intermolecular interaction in the spectral shifts. Specific solvent effects lead to essential deviation of measured points from this linear plot. 

The method of revealing of H-bonds is very simple an addition of low concentration, 1-3% of molar fraction, of alcohols (ethanol, methanol) to the solution in neutral solvent (CH, for example) results in a substantial spectral shift. Further addition of alcohols, up to 100%, gives much smaller shifts. A small percentage of alcohol may cause 50-80% of total spectral shift. Upon addition of the trace quantities of alcohol, one sees that the intensity of the initial spectrum is decreased, and new red-shifted spectrum appears. The appearance of new spectral component is a characteristic of specific solvent effects. Because the specific spectral shifts occur only at low concentration of alcohol, this effect is probably attributed to H-bonding to electronegative group in the molecule. The next experiment, which can support this conclusion, is an addition of aprotic solvent, for example,... 

Table 6.6 lists some reactions of the electron in water, ammonia, and alcohols. These are not exhaustive, but have been chosen for the sake of analyzing reaction mechanisms. Only three alcohols—methanol, ethanol, and 2-propanol—are included where intercomparison can be effected. On the theoretical side, Marcus (1965a, b) applied his electron transfer concept (Marcus, 1964) to reactions of es. The Russian school simultaneously pursued the topic vigorously (Levich, 1966 Dogonadze et al, 1969 Dogonadze, 1971 Vorotyntsev et al, 1970 see also Schmidt, 1973). Kestner and Logan (1972) pointed out the similarity between the Marcus theory and the theories of the Russian school. The experimental features of eh reactions have been detailed by Hart and Anbar (1970), and a review of various es reactions has been presented by Matheson (1975). Bolton and Freeman (1976) have discussed solvent effects on es reaction rates in water and in alcohols. 

An unusual solvent effect was observed in cycloadditions of aromatic nitrile N-oxides with alkyl-substituted p-benzoquinones in ethanol-water (60 40) the reaction rates were 14-fold greater than those in chloroform (148). The use of ion pairs to control nitrile oxide cycloadditions was demonstrated. A chiral auxiliary bearing an ionic group and an associated counterion provides enhanced selectivity in the cycloaddition the intramolecular salt effect controls the orientation of the... 

As described previously in the crystallization from ethanol (EtOH) solutions A and B polymorphs appeared. However, with kinds of the solvent the polymorphic nucleation behavior may change. In this section the solvent effect in the nucleation behavior of Pr-est is shown. 

The acid-catalysed hydrolysis of the acylal, 1-phenoxyethyl propionate (13), has been studied using the PM3 method in the gas phase. The kinetics and mechanism of the hydrolysis of tetrahydro-2-furyl and tetrahydropyran-2-yl alkanoates (14) in water and water-20% ethanol have been reported. In acidic and neutral media, kinetics, activation parameters, isotope-exchange studies, substituent effects, solvent effects and the lack of buffer catalysis pointed clearly to an Aai-1 mechanism with formation of the tetrahydro-2-furyl or tetrahydropyran-2-yl carbocation as the rate-limiting step (Scheme 1). There is no evidence of a base-promoted Bac2 mechanism up to pH 12. ... 

Solvent effects have been investigated in isatin (193) hydrolysis. Results from ethanol-water and acetonitrile-water mixtures revealed that for alkaline hydrolysis log k was correlated with the reciprocal of the dielectric constant. A tetrahedral intermediate (194) is involved, which breaks down to yield the ring-opened amino acid (195). A comparison has been made of the lability of isatin (193) towards diethyl-amine and hydroxide ion, the latter showing the greater effect. ... 

Williams and coworkers preliminarily reported that CO oxidation on Pt/Al203 is faster in the presence of water solvent than in the presence of ethanol [141]. We then studied CO oxidation on platinum surface in the presence of different solvents, and identified obvious solvent effects, namely, CO oxidation takes place the most easily with water solvent, the least easily with carbon tetrachloride solvent, and follows the overall trend of water > ethanol > methanol > cyclohexane > benzene carbon tetrachloride [67]. We subsequently took advantage of the solvent effect to design a diagnosing tool to pin down low-coverage CO at the liquid-solid interface, by flushing the liquid-solid interface with water and carbon tetrachloride individually [67]. 

Reports on solvent effects on rate constants for aquation of diimine complexes include those on [Fe(5Brphen)3] + and [Fe(4,7-Me2phen)3] " " in methanol- and ethanol-water, [Fe(bipy)3] +, [Fe(phen)3] +, and [Fe(5N02phen)3] + in aqueous methyl D-glycopyranosides, and... 

Different stereoselectivities caused by solvent effects are demonstrated in the reduction of dihydroisophorone (3,3,5-trimethylcyclohexanone) with sodium borohydride which gave less stable tranj-3,3,5-trimethylcyclohexanol (with axial hydroxyl) by reduction in anhydrous isopropyl alcohol (55-56%), in anhydrous tert-butyl alcohol (55%), in 65% aqeuous isopropyl alcohol (59.5%), in anhydrous ethanol (67%), and in 71% aqueous methanol (73%) (the balance to 100% being the more stable cis isomer with equatorial hydroxyl) [849]. 

Hexamethylphosphoramide, which is a liquid under ambient conditions, is able to solvate electrons. Mixtures of this solvent with up to 21 % ethanol are effective for the electrochemical Birch type reactions. The strong hydrogen bonding between the two solvents suppresses hydrogen evolution at die cathode [42], Benzene is reduced at constant current in this solvent to a mixture of hydrocarbons, cyclohexane being formed early in the process [43,44],... 

A calculated transition energy used to assess the polarity of a solvent. The solvent ionizing capability directly affects the position of a peak, easily measured, in the ultraviolet region of the spectrum of the complex of an iodide ion with 2-methyl- or l-ethyl-4-carbomethoxypyridinium ion. Water has a Z value of 94.6, ethanol has a value of 79.6, dimethyl sulfoxide s value is 71.1, and benzene has a value of 54. A similar polarity scale, known as x(30) values, is related to the Z value scale Z = 1.41 t(30) -E 6.92. See Solvent Effects... 

An unstable analogue of prostaglandin, PGE, formulated in a poly butadiene polymeric matrix, was placed in a SFE cell and extracted with C02/formic acid (95 5) at 15°C Extraction was continued for 60 min and then the extract was collected in hexane/ethanol (2 1) at 0"C. The advantages of the SFE method were that the solvent effected simultaneous cleavage of the polymer-prostaglandin bond without instability problems and with improved mass transfer enabling good recovery from the polymer matrix. 

Three different sets of experimental aqueous-phase pKa s allow us to judge to what extent solvent effects can be ignored and, where they cannot be ignored, assess the performance of the SMS. 4 model in accounting for solvation. The first involves a diverse set of carboxylic acids and the second a diverse series of alcohols and phenols. Calculated acidities (relative to acetic acid in the case of carboxylic acids and relative to ethanol in the case of alcohols and phenols) have been obtained from the Hartree-Fock 6-311+G model. Previous comparisons with gas-phase acidities suggest that this should be as satisfactory as any other model for this purpose (see, for example. Tables 6-18 and A6-50). 6-3IG geometries have been used in place of 6-311+G geometries in order to save computation time. (See... 

Solvent effects for a series of thienopyridine derivatives, 49, have been studied. In organic solvent/water mixtures, the values, ranging from 8.75 to 10.44, are found to be dependent on both the amount and the type of organic solvent (dimethylformamide (DMF), methanol, ethanol, and acetone) used in the mixture, with pA(a values increasing as the organic co-solvent concentration increases <2003CED1495>. 

Here, A denotes an add of type HA-, HA or BH+, and z and q denote the charge and the radius, respectively, of species i. The influence of permittivity on p/C, depends on the charges, radii and the charge locations of the add and its conjugate base. Table 3.3 shows the pKa values of some acids and add-base indicators in water, methanol and ethanol [3], The solvent effects on pK l are smaller for BH+-type adds than for HA- or HA-type acids. For the BH+-type acids, zA=l and zB=0 in Eq. (3.16), and the influence of solvent permittivity is expeded to be small. 

Table 2 shows the maxima of the K-bands of phenolic substances and their methyl ethers in hexane (or benzene) and in ethanol, as well as the displacements of the K-bands of the phenols as compared with the corresponding methyl ethers (D, Me II) in both solvents and the displacements attributable to hydrogen bond formation (D, H-bond) obtained by subtracting the solvent effect observed for the methyl etier from that observed for the corresponding phenol. 

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