Acetonitrile dipole moment

Parker37 defined class 4 as solvents "which cannot donate suitable labile hydrogen atoms to form strong hydrogen bonds with an appropriate species and proposed the designation dipolar aprotic solvents he extended their range down to s > 15 and quoted as examples acetone, acetonitrile, benzonitrile, dimethylformamide, dimethyl sulphoxide, nitrobenzene, nitromethane (41.8) and sulfolane (tetramethylene sulphone) (44), where e varies from 21 to 46.5, and the dipole moment p from 2.7 to 4.7 debye. 

It is easy to see that, for instance, water is a more polar solvent than heptane. Water has a dipole moment, is both a proton donor and acceptor and will dissolve ionic solutes. Similarly, methanol and acetonitrile are both more polar than heptane, but it is not so easy to assign relative polarities to methanol and acetonitrile. 

Compounds with high dielectric constants such as water, ethanol and acetonitrile, tend to heat readily. Less polar substances like aromatic and aliphatic hydrocarbons or compounds with no net dipole moment (e. g. carbon dioxide, dioxane, and carbon tetrachloride) and highly ordered crystalline materials, are poorly absorbing. 

A clear effect of hydrogen bonding is afforded by considering the interaction of alcohols with acetonitrile, CH3CN, and trimethylamine, (CH3)3N. The dipole moments of these molecules are 3.44D... 

With instruments based on fluorescence up-conversion (see Chapter 11) that offer the best time resolution (about 100 fs), such a fast inertial component was indeed detected in the fluorescence decayc,d). Using coumarin 153 as a solute (whose dipole moment increases from 6.5 to 15 D upon excitation), the inertial times of acetonitrile, dimethylformamide, dimethyl sulfoxide and benzonitrile were found to be 0.13, 0.20, 0.17 and 0.41 ps, respectively. ... 

The dipole moment in the excited state was estimated (by means of Eqs 7.8 and 7.9) to be 31.8 D. The fluorescence maximum is located at 407 nm in n-hexane and 697 nm in acetonitrile. Unfortunately, protic solvents cause complete quenching therefore, this family of molecules cannot be used as polarity probes in protic microenvironments. 

According to the electrostatic model the solvation is due to electrostatic interaction between the charged ions and the dipolar solvent molecules. Thus the solvating and ionizing properties of a solvent are considered as being due primarily to the dipole moment of the solvent molecules. Thus, ionic compounds such as sodium chloride are insoluble in non-polar solvents such as carbon tetrachloride. Actually, rather than the dipole moment the field action of the dipoles should be considered. This approach might explain why acetonitrile (p = 3.2) is poor in its ionizing properties compared to water (p = 1.84). However, no numerical values are available for this quantity. 

Po Polarity, Xe proton acceptor, Xd proton donor, Xn dipole moment, THF tetrahydrofuran, ACN acetonitrile, MeOH methanol, ATN acetone, DMF dimethylformamide, nc cannot be calculated. 

If the proton donor value Xd) is fixed at 2.58, the equivalent eluent is 54% aqueous acetonitrile and the predicted log/ value for the logP = 3 compounds should be 0.46, which is again different from any of the log/ values in 40% aqueous THF. The dipole moment Xn) of 40% aqueous THF was 2.20 however, such a value cannot be obtained with any proportion of aqueous acetonitrile. To obtain the same log k values as in 40% aqueous THF, a... 

Chromatographic Behaviour of log P = 3 Compounds in Aqueous Dimethylform-amide (DMF). DMF is a solvent with a strong dipole moment (Table 4.2). The same log A values in 50% aqueous DMF can be obtained at a concentration of 26% aqueous acetonitrile for ROH, 44% aqueous acetonitrile for PAH, 37% for RB, and 36% aqueous acetonitrile for ROB. When eluents with equivalent Po, Xe, Xd, or Xn values in 50% DMF were selected, different log A values were predicted in all three cases. 

From the theoretical viewpoint, acetonitrile is the most suitable solvent to study the correlation of retention times and log P values of analytes, since the dipole moment (2.44) is nearly equal to that of water (2.55) (Figure 4.4). The electron donor effect can therefore be eliminated, and the elution order is not changed on modification of the acetonitrile-water mixture ratio. The first choice of an eluent should therefore be an acetonitrile-water mixture for non-ionic compounds in reversed-phase liquid chromatography. Methanol, acetone, THF, or DMF can then be added to improve the resolution. 

Heating of 5-ethoxy-1,2,3,4-thiatriazolium tetrafluoroborate (161) with malononitrile and tri-ethylamine in acetonitrile solution gave crystalline l,2,3,4-thiatriazolium-5-dicyanomethylide (22) (Equation (13)) <79JCS(P1)744>. The structure is supported by spectral properties. The IR spectra show C=C (1500 cm ) and CN (2200 cm ) stretching vibrations and the mass spectra shows the correct molecular ions. A dipole moment of 8.8 D (R = Ph) was measured in benzene in good agreement with the proposed structure (22). 

The salts (294) with malononitrile and triethylamine in boiling acetonitrile yield the new class of meso-ionic heterocycles in which the exocyclic carbanionoid residue is a biscyanomethylene group. The diphenyl derivative (296, R = R = Ph) has a dipole moment of 9.54 D in benzene solution. ... 

Stereoselectivity. The SCF can influence the stereoselectivity as well as the regioselectivity of a cyclic enone dimerization. There are both syn and anti stereoisomers of the head-to-tail dimers of both isophorone and cyclohexenone. The differences in alignment of the cyclohexyl rings was portrayed schematically by Hrnjez et al. (31). Both HT photodimers for isophorone have similar dipole moments. Hence, a variation in solvent polarity is not expected to influence the anti/syn ratio and, indeed, these stereoisomers are formed in equal amounts regardless of the dielectric constant in liquid solvents (32). For the cyclohexenone HT stereoisomers, the anti configuration dominates in acetonitrile and benzene, but there has been limited study of stereoselectivity in other liquids. 

Absorption maxima of the open-ring form in benzene, THF, and acetonitrile were observed in the wavelengths ranging from 335 to 340 nm. Although the maximum showed a small hypsochromic shift in hexane, the solvent shift in the absorption spectrum was rather small. On the other hand, the fluorescence spectra showed remarkable Stokes shifts depending on the solvent polarity. The maximum at 488 nm in hexane shifted to 560 nm in THF. At the same time, the intensity decreased. The fluorescence intensity in acetonitrile was <1% of the intensity in hexane. The results indicate that the excited state of the open-ring form has a polar structure with a large dipole moment. 

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