Tetrachloromethane, from chlorination methane

Any combination of atomic and hybrid orbitals may overlap to form bonds. For example, the four sp orbitals of carbon can combine with four chlorine 3p orbitals, resulting in tetrachloromethane, CCI4. Carbon-carbon bonds are generated by overlap of hybrid orbitals. In ethane, CH3-CH3 (Figure 1-19), this bond consists of two sp hybrids, one from each of two CH3 units. Any hydrogen atom in methane and ethane may be replaced by CH3 or other groups to give new combinations. 

When methane and chlorine gas are mixed in the dark at room temperature, no reaction occurs. The mixture must be heated to a temperature above 300°C (denoted by A) or irradiated with ultraviolet light (denoted by hv) before a reaction takes place. One of the two initial products is chloromethane, derived from methane in which a hydrogen atom is removed and replaced by chlorine. The other product of this transformation is hydrogen chloride. Further substitution leads to dichloromethane (methylene chloride), CH2CI2 tri-chloromethane (chloroform), CHCI3 and tetrachloromethane (carbon tetrachloride), CCI4. 

This reaction is not really suitable for preparing specific halogenoalkanes, because we get a mixture of substitution products. In the reaction between methane and chlorine, the products can include dichloromethane, trichloromethane and tetrachloromethane as well as chloromethane. These other products result from propagation steps in which a chlorine free radical attacks a halogenoalkane already formed. For example ... 

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