Solvent acceptor

Proton-acceptor solvents are preferred at the donor solute separation and vice versa. 

In good electron acceptor solvents, such as carbon tetrachloride and chloroform, the photodegradation of carotenoids is significantly increased as compared to other solvents (Christophersen et al. 1991, Mortensen and Skibsted 1999), because of a direct photoinduced electron-transfer reaction from the excited singlet state of the carotenoids to the solvent, as determined by transient absorption spectroscopy (Jeevarajan et al. 1996, Mortensen and Skibsted 1996,1997a,b, El-Agamey et al. 2005), Equation 12.2 ... 

The different solvation energetics of R and R- will also lead to errors in the bond dissociation enthalpies calculated with equation 16.33. For instance, in the case of phenol, whose interactions with proton-acceptor solvents (like DMSO) are obviously stronger than those for the phenoxy radical, a negative correction should be applied to the value of Z)//°(PhO-H) calculated from equation 16.33 (see also equation 16.32). It is probably unwise to ascribe the 7 kJ mol-1 difference between the electrochemical and the recommended DH° (PhO—R) value to the differential solvation effects. Although this discrepancy is in the correct direction, it lies within the suggested uncertainty of the method. 

When (5(15N) values for the previously used series of 13 para-substituted anilines were measured in acetone42, a significantly weaker hydrogen-bond acceptor solvent than DMSO, a smaller shift dependence on para TT-electron-acceptor substituent solvation (SSAR) effects in acetone was observed (Table 10). This reduction42 was expressed by the (rather unsatisfactory) forms, 4 and 5. 

A-(/>-Nitrophenyl)alkylenediamines 18 form intramolecular hydrogen bonds between the two N—H groups (aromatic and aliphatic) as reported in equilibrium 9. When hydrogen bond acceptor solvents are used, intramolecular hydrogen bonds are formed between 18 and solvents, but when the nitro group is in the ortho position, the hydrogen bond is formed between the aromatic amino and nitro groups. 

Acceptor solvents, which tend to react with electron pair donors. 

The different behaviour of HC104 and Ph3 COH in both water and sulfuric acid can now be interpreted Perchloric acid, which has pronounced acceptor properties, reacts readily and completely with the donor solvent water and ionization occurs but there is no interaction with the acceptor solvent sulfuric acid and, hence, no ionization is observed in the latter solvent. Triphenylcarbi-nol, on the other hand, reacts with the acceptor sulfuric acid and not with the donor solvent water. 

N-methylaniline orgchem C6H5NH(CH3) Oily liquid, colorless to reddish-brown soluble In water and organic solvents bolls at 190°C used as an acid acceptor, solvent, and chemical Intermediate. en jmeth-al an-a-lan ci-methylanisalacetone org chem CH30C6H4CH CHC0CH2CH3 A white to pale yellow, combustible solid with a melting point of 60°C used as a flavoring. al-f3 meth-3l,an-3-s3 las-3 ton ... 

Proton donor Proton acceptor Solvent Precipitation Ref. 

A tew, the nonmetal oxides and halides, can behave as acceptor solvents, reacting with anions and other basic centers ... 

Other. The pyridines and methylpvridines and their mixtures are used as chemical processing aids (e.g.. acid acceptors, solvents) and as industrial corrosion inhibitors. 

IR data have indicated93 that (29 R = Ac, cyclohexyl, MeS02, Me, H R7 = Pr, Bu R" = Me, Ph) exist as tautomer (29) in the crystalline state and in proton acceptor solvents and as tautomer (30) in proton donating solvents. 

According to deuterium-induced upfield H NMR isotope shifts in partially deuterated rigid cyclohexane-1,3-diols dissolved in CDC13 or benzene-c/6, the OH is preferentially solvent-exposed, while deuterium prefers to reside in the intramolecular hydrogen bond (49).121 In acetone-c/6 and DMSO-c/6 downfield isotope shifts indicate that the OH preferentially resides in the intramolecular hydrogen bond, while OD forms an external hydrogen bond to the acceptor solvent, S (50). 

In contrast, a partially deuterated rigid 1,4 diol shows upfield isotope shifts not only in CDC13 but also in acetone- and DMSO-i/fr 122 Again the OH is preferentially solvent-exposed in CDC13, while deuterium prefers to reside in the intramolecular hydrogen bond. Again the OD is preferentially solvent exposed in acetone- and DMSO-d6, while OH prefers to reside in the intramolecular hydrogen bond. The paradoxical commonality of upfield isotope shifts is due to a reversal of the chemical shifts of interior and exterior sites of 1,4 diols in acceptor solvents. The equilibrium constant in DMSO-d6 is... 

Compound 156 adopted the 3H tautomer exclusively, even in hydrogen bond acceptor solvents, such as acetone-46. It was proposed by analogy with the 1,5-benzodiazepine system which adopts an analogous tautomer, the seven-membered ring of 156 is likely to be nonplanar and, regarding NMR spectra, interconversion between two equivalent forms may be present. 

Radical fragmentation of 2-nitrophenyl-azo-trityl resin was studied in the presence of various radical acceptor solvents to elucidate possible radical reaction pathways. When using benzene as solvent, only 2-nitro-bi-phenyl was formed as the product of radical substitution reaction (SNR) in 67% yield. Hydrogen-radical abstraction from the polymer backbone (e.g., from the benzylic units of polystyrene) was completely suppressed. When toluene was used as solvent, a mixture of the following products was obtained nitrobenzene, 4-methyl-2 -nitrobisphenyl, 2-methyl-2 -nitro-bisphenyl, and 3-methyl-2 -nitrobisphenyl (9 9 1 1). In the case of toluene, the nitro-aryl radicals undergo H-abstraction with radical substitution as a competing reaction pathway. These results indicate that H-abstraction... 

Although solvents may be classified as donor solvents (Lewis bases) and acceptor solvents (Lewis acids), most of the more widely used nonaqueous solvents are donor solvents. Some acceptor solvents, such as S02, BrF3, AsC13, or the liquid hydrogen halides, have proved to be useful in coordination chemistry.13"16 Ionization is promoted in a donor solvent by solvation of cations and in an acceptor solvent by solvation of anions. For example, arsenic(m) iodide is ionized in a donor solvent D according to the reaction... 

The theory for this intermolecular electron transfer reaction can be approached on a microscopic quantum mechanical level, as suggested above, based on a molecular orbital (filled and virtual) approach for both donor (solute) and acceptor (solvent) molecules. If the two sets of molecular orbitals can be in resonance and can physically overlap for a given cluster geometry, then the electron transfer is relatively efficient. In the cases discussed above, a barrier to electron transfer clearly exists, but the overall reaction in certainly exothermic. The barrier must be coupled to a nuclear motion and, thus, Franck-Condon factors for the electron transfer process must be small. This interaction should be modeled by Marcus inverted region electron transfer theory and is well described in the literature (Closs and Miller 1988 Kang et al. 1990 Kim and Hynes 1990a,b Marcus and Sutin 1985 McLendon 1988 Minaga et al. 1991 Sutin 1986). 

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