Tetrachloromethane dipole moment

If the four atoms attached to the central atom in a tetrahedral molecule are the same, as in tetrachloromethane (carbon tetrachloride), CCI4 (30), the dipole moments cancel and the molecule is nonpolar. However, if one or more of the atoms are replaced by different atoms, as in trichloromethane (chloroform), Cl ICI, or by lone pairs, as in NH3, then the dipole moments associated with the bonds are not all the same, so they do not cancel. Thus, the CHCI, molecule is polar (31). 

Exercise 24-16 Would you expect the dipole moment measured for 1,3,5-trinitrobenzene in 1,3,5-trimethylbenzene solution to be the same as in tetrachloromethane solution Explain. 

In contrast with water and ammonia, carbon dioxide and tetrachloromethane (CCI4) have zero dipole moments. Molecules of both substances contain individual polar covalent bonds, but because of the symmetry of their structures, the individual bond polarities exactly cancel. 

Nonpolar compounds Chemical species without significant dipole moments, such as most hydrocarbons, and some very symmetric compounds such as tetrachloromethane and hexafluorobenzene. 

From the foregoing discussion, the propensity of a sample to undergo micro-wave heating is related to its dielectric and physical properties. Compounds with high dielectric constants (e.g. ethanol and dimethylformamide) tend to absorb microwave irradiation readily whereas less polar substances (for example aromatic and aliphatic hydrocarbons) or compounds with no net dipole moment (e.g. carbon dioxide, dioxane, and tetrachloromethane) and highly ordered crystalline materials, are poorly absorbing. 

As already mentioned, chlorides of methane are very useful solvents. From the knowledge about the polarity of molecules, i.e. their dipole moments, we can distinguish between polar and nonpolar solvents. The polar solvents are for example CH2CI2 and CHCI3, while tetrachloromethane, CCI4, is a nonpolar solvent. Polarity of solvents is one of the most important properties, not only for practical laboratory applications, but also for the theory of reaction mechanisms, reactivity and selectivity of organic compounds. 

Account for the fact that among the chlorinated derivatives of methane, chloromethane has the largest dipole moment and tetrachloromethane has the smallest dipole moment. 

The tetrachloromethane molecule is non-polar. Based on the electronegativity difference between carbon and chlorine, the carbon-chlorine bonds are polar. The resultant dipole moment is zero, which means that the dipoles must be oriented in such a way that they cancel each other. The tetrahedral arrangement of the four chlorine atoms around the central carbon atom provides the symmetrical distribution of bond dipoles that leads to this vectorial cancellation (Figure 4-52). Consequently, the tetrachloromethane molecule is non-polar. 

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