Dimethyl sulfoxide Dipole moments

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. ... 

An analysis of the Wannier functions in CPMD simulations of one dimethyl sulfoxide (DMSO) molecule dissolved in water was carried out by us in 2004 in order to gain more insight into the unusual properties of the DMSO-water mixture (72). In this special case, we have utilized MLWCs to calculate molecular dipole moments of the DMSO molecule in gas phase and aqueous solution. Comparing those two a large increase of the local dipole... 

Theoretical calculations on the /Fdithietane 1,3-dioxide 3 =, sy -dithietane 1,3-dioxide 4 equilibrium in the gas phase at HF/6-31G level show that the anti-isomer 3 is slightly favored (by ca. 0.27 kcal moF1) over the, sy -isomer 4. The antijsyn-ratio is 1.6, with a ry -concentration of 36%. Due to different dipole moments of the anti 3 and syn 4, the solvents of low and medium-high polarity such as carbon tetrachloride, acetonitrile, and dimethyl sulfoxide (DMSO) exert a strong influence on the antisyn interconversion, producing an increase in the ry -concentration <2001BOC57>. 

Polar aprotic solvents, on the other hand, have dipole moments and are still able to solvate cations by electron donation from an oxygen atom, but they lack the ability to form hydrogen bonds because any hydrogen atoms they may have are on carbon. Examples include DMF and DM So (dimethyl sulfoxide). 

In contrast, dipolar aprotic solvents possess large relative permittivities (sr > 15), sizeable dipole moments p > 8.3 10 ° Cm = 2.5 D), and average C.f values of 0.3 to 0.5. These solvents do not act as hydrogen-bond donors since their C—H bonds are not sufficiently polarized. However, they are usually good EPD solvents and hence cation sol-vators due to the presence of lone electron pairs. Among the most important dipolar aprotic solvents are acetone, acetonitrile [75], benzonitrile, A,A-dimethylacetamide [76, 77], A,A-dimethylformamide [76-78], dimethylsulfone [79], dimethyl sulfoxide [80-84], hex-amethylphosphoric triamide [85], 1-methylpyrrolidin-2-one [86], nitrobenzene, nitro-methane [87], cyclic carbonates such as propylene carbonate (4-methyl-l,3-dioxol-2-one) [88], sulfolane (tetrahydrothiophene-1,1-dioxide) [89, 90, 90a], 1,1,3,3-tetramethylurea [91, 91a] and tetrasubstituted cyclic ureas such as 3,4,5,6-tetrahydro-l,3-dimethyl-pyr-imidin-2-(l//)-one (dimethyl propylene urea, DMPU) [133]. The latter is a suitable substitute for the carcinogenic hexamethylphosphoric triamide cf. Table A-14) [134]. 

Whereas in the gas phase and in nonpolar solvents sueh as tetraehloromethane and benzene, the 2-azidothiazole (38a) is the more stable isomer, in polar solvents such as dimethyl sulfoxide and hexamethylphosphorie triamide the bieyelie valenee isomer (38b) is the dominant speeies [100]. This result is in line with the faet that the dipole moment of phenyl azide g = 5.2 10 Cm) is smaller than that of cyclie 1,2,3-benzotriazole (// = 13.7 10 Cm). Similar results have been obtained for the valenee isomers of 3-azidopyrazine-l-oxide [204]. 

These results are supported by the observation that dipolar non-HBD solvents such as A,A-dimethylformamide or dimethyl sulfoxide, in spite of their high relative permittivities (36.7 and 46.5) and their high dipole moments (12.3 10 and 13.0-10 Cm), favour neither the ionization of haloalkanes nor SnI reactions cf. Section 2.6). Dipolar non-HBD solvents cannot act as hydrogen-bond donors and are therefore poor at solvating the departing anions. Thus, the anchimerically assisted ionization of 4-methoxyneophyl tosylate, shown in Eq. (5-102), is nine times faster in acetic acid than in dimethyl sulfoxide. This is in spite of the fact that the relative permittivity of acetic acid is eight times smaller than that of dimethyl sulfoxide also the dipole moment of acetic acid is smaller than that of dimethyl sulfoxide [265],... 

The density of sucrose is 1.5879 g/cm . The linear expansion coefficient ranges from 0.0028 to 0.0050 percent, depending on the axis. Characteristic infrared (IR) absorption bands occur at 1010, 990, 940, 920, 870, 850 cm (sharp), and at 680, 580 cm" (broad). The specific heat of crystalline sucrose is 415.98 J/mol at 20°C. The dipole moment is 2.8 x 10" cm (8.3D). Sucrose is readily soluble in water and the solubility increases with the rise in temperature. It is sparingly soluble in alcohol but moderately soluble in organic solvents, such as dimethyl formamide, p5nidine, and dimethyl sulfoxide. 

Aprotic polar liquids such as dimethyl sulfoxide and acetonitrile make up another group. These molecules have high dipole moments, so that dipole-dipole interactions are an important part of the description of intermolecular forces. 

Estimate the contributions to the van der Waals energy in dimethylsulfoxide at 25° C by considering two molecules in contact as hard spheres with diameters of 491 pm. The dipole moment of dimethyl sulfoxide is 3.96 debyes, its polarizability, 7.99 X 10 nm, and its ionization potential, 9.01 eV. 

The stmcture, stereochemistry, and potential conformational equilibria (Scheme 1) of 1,3,2-dioxathian 12 have not yet been studied theoretically but ab initio molecular orbital (MO) calculations at the MP2 level of its 2-oxide 13, both in the gas phase and in various solvents, have been reported <2000JP0187>. In the gas phase and in low-polarity solvents, 13-ax proved to be the only conformer present. In medium-polarity solvents such as acetonitrile or dimethyl sulfoxide, the equatorial counterpart 13-eq is of importance and participates up to 12% in the conformational equilibrium. In addition, both the dipole moments (/ii3.ax = 3.87 D /ti3 eq = 6.57 D) and the S=0 stretching vibrations (13-ax 1177-1180 cm ... 

The dissolution behavior of a solvent cannot be predicted solely on the basis of its dipole moment. For example, dioxane (/t = 0.4 D) is a very good solvent and has a comparable solvency to dimethyl sulfoxide (/t = 4.0 D). 

Polarity Polarity is the ability to form two opposite centers in the molecule. The concept is used in solvents to describe their dissolving capabilities or the interactive forces between solvent and solute. Because it depends on dipole moment, hydrogen bonding, entropy, and enthalpy, it is a composite property without a physical definition. The dipole moment has the greatest influence on polar properties of solvents. Highly symmetrical molecules (e.g. benzene) and aliphatic hydrocarbons (e.g. hexane) have no dipole moment and are considered non-polar. Dimethyl sulfoxide, ketones, esters, alcohol are examples of compounds having dipole moments (from high to medium, sequentially) and they are polar, medium polar, and dipolar liquids. 

Dimethyl sulfoxide is a very polar, high dipole moment, strong hydrogen bond accepting solvent It is has a high viscosity nearly equal to that of IPA. Typical impurities from the manufacturing process include dimethyl sulfide (from whidi DMSO is commonly manufactured) and dimethyl sulfone. Decomposition products include dimethyl sulfide, dimethyl sulfone, methyl mercaptan, and bis(methylthio> methane [1552]. 

The layers of phyllodisilicic acids H2Si205 and of dehydrated forms of other acids are held together by hydrogen bonds and van der Waals interactions. To separate the layers, the guest molecules have to disrupt hydrogen bonds. This requires guest molecules with high dipole moments acid amides 3.6-3.8 Debye, dimethyl sulfoxide 4 Debye, AA -dimethyl urea 4.8 Debye. Molecules with di-... 

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