Chloromethane molecule, dipole moment

Carbon-oxygen and carbon-halogen bonds are polar covalent bonds and carbon bears a partial positive charge in alcohols ( " C—0 ) and in alkyl halides ( " C—X ) Alcohols and alkyl halides are polar molecules The dipole moments of methanol and chloromethane are very similar to each other and to water... 

Before looking at the forces between molecules, it s first necessary to develop the ideas of bond dipoles and dipole moments. We saw in Section 7.4 that polar covalent bonds form between atoms of different electronegativity. Chlorine is more electronegative than carbon, for example, and the chlorine atom in chloromethane (CH3C1) thus attracts the electrons in the C C1 bond toward itself. The C-Cl bond is therefore polarized so that the chlorine atom is slightly electron-rich (8—) and the carbon atom is slightly electron-poor (<5+). 

It s relatively easy to measure dipole moments experimentally, and values for some common substances are given in Table 10.1. Once the dipole moment is known, it s then possible to get an idea of the amount of charge separation in a molecule. In chloromethane, for example, the experimentally measured dipole moment is /x = 1.87 D. If we assume that the contributions of the nonpolar C-H bonds are small, then most of the chloromethane dipole moment is due to the C-Cl bond. Since the C-Cl bond distance is 178 pm, we can calculate that the dipole moment of chloromethane would be 1.78 X 4.80 D = 8.54 D if the C-Cl bond were ionic (that is, if a full negative charge on chlorine were separated from a full positive charge on carbon by a distance of 178 pm). But because the measured dipole moment of chloromethane is only 1.87 D, we can conclude that the C-Cl bond is only about (1.87/8.54)(100%) = 22% ionic. Thus, the chlorine atom in chloromethane has an excess of about 0.2 electron, and the carbon atom has a deficiency of about 0.2 electron. 

Non-polar. A solvent in which the molecules do not possess a permanent dipole moment and consequently will solvate non-polar species in preference to polar species. For example, benzene and tetra-chloromethane are good solvents for iodine and paraffin wax, but do not dissolve sodium chloride. 

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. 

Molecular models for chloromethane, dichloromethane, and trichloromethane are given to show the direction of the dipole of molecule more clearly. Calculated dipoles for these three molecules are 2.87, 2.50, and 1.72 Debye, respectively, and it is clear that the directional nature of the individual bond dipoles plays a role in the overall magnitude of the dipole moment for the molecrde. With three chlorine atoms directed to different regions of space, chloroform is the least polar of the three molecules, despite the presence of three polarized bonds. 

One liquid for which the value of seems suspect is 1-bromonaphthalene. It contains a polar carbon-bromine bond. I have not been able to find the dipole moment of 1-bromonaphthalene, but the values for bromobenzene, chlorobenzene and fluorobenzene which are chemically similar to 1-bromonaphthalene are 1.70 D, 1.69 D and 1.60 D, respectively. These molecules are almost as polar as chloromethane (1.97 D) and bromomethane (1.81 D), where the polarity of the... 

Both chloromethane, CH3CI, and formaldehyde, CH2O, have polar bonds and, because of their geometries, are polar molecules. Because of its linear geometry, acetylene, C2H2, has no dipole moment. The experimentally measured dipole moments are shown. The electrostatic potential map (elpot) of formaldehyde clearly shows this charge distribution. ... 

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