Acetone molecular dipole moment

Of these, probably the most decisive are type 2 and the combination of types 1 and 3. It is difficult to rationalize the weak H bonds formed by acetonitrile as a base (molecular dipole moment of 3.44 d) and the strong H bonds formed by trimethylamine (molecular dipole moment of 0.7 d) together with the interpretation that an acid A—H forms H bonds with these bases because of the electrostatic interaction of the A—H dipole with point charges on the nitrogen atoms. Another interesting comparison is afforded by the approximately equal H bond properties of acetone, diethyl ether, and dioxane, with dipole moments of 2.85 D, 1.15 D, and 0.4 d, respectively. These qualitative discrepancies can be backed by a substantial body of quantitative data. Table 8-1 collects some of these data, and verifies the absence of any systematic dependence of enthalpy of H bond formation upon the molecular dipole moment. Compilations of At, (814) and of AFshow that these properties are similarly unrelated to /i- Certainly these data show that the strength and behavior of a H bond are not determined in a direct way by the dipole moment. This lack of dependence is not easily reconciled with... 

Physical Properties Sulfur mustard (mustard gas) is a colorless oil with bp of 227°C, mp of 14°C, molecular dipole moment 1.78 D (hexane), and molecular mass of 159. It normally is encountered as an impure, pale yellow-brown, odoriferous liquid. The color generally deepens with increasing amounts of impurity. HD has a vapor density of 5.4 relative to air and a vapor pressure of 0.072 mm Hg at 20°C. As a liquid, it is slightly denser than water (1.27 g/mL at 20°C). It is miscible in typical organic solvents (e.g., carbon tetrachloride, acetone or chloroform) but has a lower solubility in water (0.092 g/100 g at 22°C) (Sidell et al., 1998 Somani, 1992). 

A classification scheme for molecular polarity can be based on the electric potential surrounding the molecule. Traditionally, schemes for ranking molecular polarity are based on electronegativity differences, on molecular dipole moments, or on solubility. The root-mean-square (rms) value of the molecular electric potential can be used for this purpose. Table 1 shows a ranking of 24 small molecules according to their rms electric potential. Note that all of the amides are extremely polar by this criterion, more polar than formaldehyde or water. Hydrogen fluoride is less polar than acetone, acetaldehyde, water, or the amides. At the low end of the polarity scale, the amines are surprisingly nonpolar. As expected acetylene is more polar than ethylene, which is more polar than methane. 

Acetone and 2-methylpropane have similar molecular shapes, but acetone has a large dipole moment resulting from its polar CDO bond. 

Not surprisingly, the strength of a given dipole-dipole interaction depends on the sizes of the dipole moments involved. The more polar the substance, the greater the strength of its dipole-dipole interactions. Butane, for instance, is a nonpolar molecule with a molecular mass of 58 amu and a boiling point of —0.5°C, while acetone has the same molecular mass yet boils 57°C higher because it is polar. 

Polarity is the extent to which a substance, at molecular level, is characterized by a non-symmetrical distribution of electron density. Polarity is often expressed as dipole moment, which is a function of the magnitude of the partial charges on the molecule, and the distance between the charges. Substances that have larger dipole moments have greater polarity than substances with lower dipole moments. Water and acetone, for example, have dipole moments of 1.85 and 2.80, respectively. Benzene and carbon tetrachloride are nonpolar and have dipole moments of zero. 

Paying attention to pure acetone, Brodka and Zerda have calculated rotational relaxation times and translational diffusion coefficients by molecular dynamics simulations. In particular, the calculated rotational times of flie dipole moment can be compared with a molecular relaxation time Xm obtained from the experimentally determined Xb by using the following expression, which considers a local field factor ... 

Ketones are solvents of moderate polarity. Like ethers, they are hydrogen bond acceptors and have dipole moments intermediate between those of ethers and alcohols. Ketones have a wide range of solubilities with water, from acetone being miscible, to methyl ethyl ketone (2-butanone) being soluble at 27%, to methyl propyl ketone (2-pentanone) being soluble to the 6% level. The higher molecular weight ketones are soluble to the 2% level or less. Ethyl acetate is soluble at the 9% level. 

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