Carbon tetrachloride molecular dipole moment

FIGURE 1.7 Contri bution of individual bond dipole moments to the molecular dipole moments of (a) carbon tetrachloride (CCU) and (b) dichloro-methane (CH2CI2). 

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). 

In chloromethane, the tetrahedral shape is clear, but there is only one polarized bond and the dipole for the molecule is easily predicted. In dichloromethane, however, there are two bond moments, and the dipole for the molecrde is the vector sum of these two bond moments (magnitude and direction). The dipole is shown. For trichloromethane (chloroform), the magnitude and direction of the three polarized C-Cl bonds lead to the molecular dipole moment shown. Carbon tetrachloride is interesting. There are four C-Cl bonds with equal bond polarization and dipole moments. Summing all four dipole moments for the bonds, which are directed to the corners of a regular tetrahedron, leads to a dipole moment of zero because the magnitudes of the individual bond moments cancel. 

Table 1.5 shows experimentally observed molecular dipole moments (at 20°C) for several common solvents. Notice that carbon tetrachloride (CCI4), has no molecular dipole moment. In this case, the individual dipole moments cancel each other completely to give the molecule a zero net dipole moment (p, = 0). This example (Figure 1.47) demonstrates that we must take geometry into account when assessing molecular dipole moments. 

The unequal distribution of charge produced when elements of different electronegativities combine causes a polarity of the covalent bond joining them and, unless this polarity is balanced by an equal and opposite polarity, the molecule will be a dipole and have a dipole moment (for example, a hydrogen halide). Carbon tetrachloride is one of a relatively few examples in which a strong polarity does not result in a molecular dipole. It has a tetrahedral configuration... 

Water freezes to ice at 0°C expands by about 10% on freezing boils at 100°C vapor pressure at 0°, 20°, 50°, and 100°C are 4.6, 17.5, 92.5, and 760 torr, respectively dielectric constant 80.2 at 20°C and 76.6 at 30°C dipole moment in benzene at 25°C 1.76 critical temperature 373.99°C critical pressure 217.8 atm critical density 0.322 g/cm viscosity 0.01002 poise at 20°C surface tension 73 dynes/cm at 20°C dissolves ionic substances miscible with mineral acids, alkalies low molecular weight alcohols, aldehydes and ketones forms an azeotrope with several solvents immiscible with nonpolar solvents such as carbon tetrachloride, hexane, chloroform, benzene, toluene, and carbon disulfide. 

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. 

Molecules of 1,3,5-trinitrobcnzene or p- dinitrobenzene have no electric dipole moments but they have moments in solutions where molecular compounds are formed. For example they have no moments in carbon tetrachloride or chloroform, but they do have moments in benzene, naphthalene, or dioxane. 

The dipole moment of NMA has been calculated from vapor phase measurements23 to be 3.71 D. This compares reasonably well with 3.82 D as determined from dilute solutions of NMA in benzene23 and with 3.6 D as determined from dilute solutions in carbon tetrachloride24. These values are somewhat lower than the earlier values obtained from more concentrated solutions of NMA in dioxane and carbon tetrachloride by Mizushima et al.2S. The vector moment of NMA is 3.6 D26 based on the molecular structure determined by electron diffraction18. ... 

In these two cases the dipole arrows cancel each other out because of the shape of the molecules. The linear shape of the molecule of carbon dioxide puts the dipole arrows in opposite directions to counterbalance each other. The same holds true for the tetrahedral molecular geometry found in carbon tetrachloride. Despite having polar bonds, these two molecules are nonpolar. There is no overall dipole moment in these molecules because the dipole arrows are of the same magnitude but lie in opposite directions in the molecule. This counterbalance causes the molecule to be nonpolar. 

The dipole moment of pyrazine 1-oxide has been determined in benzene at 25° as 1.66D, and comparison with those obtained by SMO (simple molecular orbitals) calculations show that agreement is good (748). Other determinations of dipole moment were as follows pyrazine 1-oxide, 1.60 (carbon tetrachloride, 25°) (749) and 1.62 (benzene, 25°) (663) 2,5- and 3,5-dimethylpyrazine 1-oxides, 1.68 and 2.14, respectively (benzene, 25°) (663) 2-phenylpyrazine 1-oxide, 1.39 (benzene, 25°) (733a) and 3-phenylpyrazine 1-oxide, 2.03 (benzene, 25°) (733a). 

Finally, non-polar molecular liquids, such as carbon tetrachloride and the hydrocarbons, form a group. Many of these systems possess no permanent dipole moment so that the intermolecular forces are similar to those existing in simple atomic liquids such as liquid argon. However, internal modes of motion are important in describing the properties of the molecular liquid. 

The zirconium tetrahalides react with esters to form ZrX4 2 ester adducts (302, 303, 330, 407-410, 412) in which, coordination number six is attained. On the basis of dipole moments (Table XIII), it is concluded that the adducts have the cis structure. This has been supported, at least in the case of ZrCl4 2011300 0 02115, by the infrared spectrum (330). Oryoscopic studies in benzene solution of the 2 1 adducts of zirconium tetrachloride and ethyl formate, ethyl acetate, and ethyl butryrate show that these complexes tend to decompose to the 1 1 species, the extent of dissociation increasing with the number of carbon atoms in the acid radical. The estimated dissociation constant is about 5 x 10", whereas for the ethyl acetate adduct of zirconium tetrabromide it is only 2 X 10". The approximate dissociation constant of the complex zirconium tetraiodide 2 ethyl acetate is 3.5 x 10". The 1 1 species were synthesized by direct reaction in benzene with strictly stoichiometric ratios of the reactants. Oryoscopic determination of molecular weights of the 1 1 complexes indicate that these complexes generally... 

The force constant of the Si—Si bond has been calculated as 1.3 x 10 dynes cm however, it is believed that this value is probably in error (f04). The dipole moments of several aromatic disilanes have been reported (2) which allowed one to calculate an aryl—Si—aryl valence angle of 115°. The dipole moment of 1,2-dichlorotetramethyldisilane was found (105) to be 1.75 debye in carbon tetrachloride and 1.35 debye in benzene. On the basis of the dipole moments, the infrared and the Raman spectra (in the gas, liquid, and solid state), information on the rotation about the Si—Si axis in 1,2-dichlorotetramethyldisilane was obtained. In the solid state, the chlorine atoms assume the tram position, whereas in the liquid and gas state the molecule exerts torsional oscillations about the Si—Si axis to a certain extent. The phase transformations of hexamethyldisilane were studied by NMR (80) and thermodynamically by means of differential thermal analysis (25). From such studies it appears that at higher temperatures rotations about both the Si—Si and Si—CH3 axes occur in combination with the overall molecular rotation about the molecular axis, whereas at lower temperatures all movements are hindered except for the Si—CH3 axial rotation. 

CCI4. Carbon tetrachloride molecules are nonpolar. Based on the electronegativity difference between Cl and C, we expect a bond dipole for the C—Cl bond. The fact that the resultant dipole moment is zero means that the bond dipoles must be oriented in such a way that they cancel. The tetrahedral molecular geometry of CCI4 provides the symmetrical distribution of bond dipoles that leads to this cancellation, as shown in Figure 10-16(a). Can you see that the molecule will be polar if one of the Cl atoms is replaced by an atom with a different electronegativity, say H In the molecule, CHCI3, there is a resultant dipole moment (Fig. 10-16b). 

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