Acetonitrile, hydrogen bond formation

Measurements of the free acid Ti vibrational lifetimes were also monitored as a function of base concentration (e.g., pyrrole with acetonitrile) to determine the effect of collisions and hydrogen-bond formation rates. Stern-Volmer plots of 1 /T1 rates versus base concentration enabled extraction of a bimolecular rate constant (kbm) for pyrrole acetonitrile of 2.5 0.2 x 1010 dm3/mol-s, which is slightly larger than the estimated Stokes-Einstein diffusion coefficient (0.73 x... 

Detection of CO2-" anion radical was conducted with a Pb electrode in CO2 saturated aqueous, acetonitrile and propylene carbonate electrolytes during cathodic polarization by ultraviolet (UV) spectroscopic measurements by Aylmer-Kelly et al. CO2- anion radical is mostly present freely in both aqueous and nonaqueous electrolyte solutions. Stabilization of CO2- due to hydrogen bond formation in aqueous electrolyte solution was suggested on the basis of the red shift of the observed absorption band. 

Obviously, this shift implies the self-association of DMSO. Further frequency shifts to even lower wave numbers (1050-1000 cm " ) are observed in both aprotic polar and protic solvents. In aprotic solvents such as acetonitrile and nitromethane, the association probably takes place between the S—O bond of DMSO and the —C=N or the —NOz group in the molecules by dipole-dipole interaction as shown in Scheme 331,32. Moreover, the stretching frequency for the S—O bond shifts to 1051 cm 1 in CHC13 and to 1010-1000 cm -1 in the presence of phenol in benzene or in aqueous solution33. These large frequency shifts are explained by the formation of hydrogen bonds between the oxygen atom in the S—O bond and the proton in the solvents. Thus, it has been... 

The addition of water and a non-hydrogen-bonding solvent to the reduction medium causes the reactions to shift toward the formation of alcohol products.313 For example, triethylsilane in a mixture of concentrated hydrochloric acid and acetonitrile (5 4) reduces 1-heptanal to 1-heptanol in quantitative yield after 3 hours at room temperature. In a mixture of triethylsilane in sulfuric acid, water, and acetonitrile (2 2 5), //-hep(anal gives a 97% yield of the same alcohol after 1.25 hours (Eq. 156).313... 

Product 34 predominates in the polar aprotic solvent (acetonitrile), while in the polar protic solvent (methanol) products 35 are formed preferentially. The different products are caused by the relative rate of deprotonation against desilylation of the aminium radical, that is in turn governed by the action of enone anion radical in acetonitrile as opposed to that of nucleophilic attack by methanol. In an aprotic, less silophilic solvent (acetonitrile), where the enone anion radical should be a strong base, the proton transfer is favoured and leads to the formation of product 34. In aprotic solvents or when a lithium cation is present, the enone anion radical basicity is reduced by hydrogen bonding or coordination by lithium cation, and the major product is the desilylated 35 (Scheme 4). 

Another example is the separation of several sulfonamides in acetonitrile by adding silver ions. Compounds such as N-containing heterocyclics were found to build selective charge transfer complexes with Ag+, which improves the selectivity of the separation. Phenols, carboxylic acids, and alcohols interact with anions such as CIO, BE, NO, Cl t,SO , and Cl in acetonitrile as solvent. The resulting electrophoretic mobility of the weak Bronsted acids (HA) in the presence of such anions is the result of the formation of complexes of the type [X. .. HA] due to the formation of hydrogen bonds (13). 

Macrocyclic receptors have also been found to complex neutral substrates,21 and complexes of both variable and exact stoichiometries have been prepared. The latter category includes acidic CH— and NH— or polar neutral molecules, such as acetonitrile, nitromethane, benzyl chloride and dimethylmalonitrile. X-Ray data indicate complex formation to be mainly a result of hydrogen bonding and dipole-dipole interactions. Section 21.3.8 contains a more detailed treatment of these complexes. 

Rate and equilibrium constants have been reported for the reactions of butylamine, pyrrolidine, and piperidine with trinitrobenzene, ethyl 2,4,6-trinitrophenyl ether, and phenyl 2,4,6-trinitrophenyl ether in acetonitrile, hi these reactions, leading to cr-adduct formation and/or nucleophilic substitution, proton transfer may be rate limiting. Comparisons with data obtained in DMSO show that, while equilibrium constants for adduct formation are lower in acetonitrile, rate constants for proton transfer are higher. This probably reflects the stronger hydrogen bonding between DMSO and NH+ protons in ammonium ions and in zwitterions.113 Reaction of 1,3,5-trinitrobenzene with indole-3-carboxylate ions in methanol has been shown to yield the re-complex (26), which is the likely precursor of nitrogen- and carbon-bonded cr-adducts expected from the reaction.114 There is evidence for the intermediacy of adducts similar to (27) from the reaction of methyl 3,5-dinitrobenzoate with l,8-diazabicyclo[5.4.0]undec-8-ene (DBU) cyclization eventually yields 2-aminoindole derivatives.115... 

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