Functional Groups and Organic Reactions

TABLE 7.3 Common Functional Groups Functional Group Type of Compound Examples 

One of the simplest functional groups consists of a single halogen atom, which we take to be chlorine for illustrative purposes. The chlorine atom forms a a bond to a carbon atom by overlap of its 3p orbital with a hybridized orbital on the carbon. The hybridized orbital may be sp, sp, or sp depending on the bonding in the hydrocarbon frame. Alkyl halides form when mixtures of alkanes and halogens (except iodine) are heated or exposed to light. 

The mechanism is a chain reaction (see description in Section 18.4). Ultraviolet light initiates the reaction by dissociating a small number of chlorine molecules into highly reactive atoms. These atoms take part in linked reactions of the following form  

Adding chlorine to C = C bonds is a more important industrial route to alkyl halides than the free-radical reactions just described. Billions of kilograms of 1,2-dichloroethane (commonly called ethylene dichloride) are manufactured each year, making this compound the largest volume derived organic chemical. It is made by adding chlorine to ethylene over an iron(III) oxide catalyst at moderate temperatures (40-50°C), either in the vapor phase or in a solution of 1,2-dibromoethane  

Almost all of the 1,2-dichloroethane produced is used to make chloroethylene (vinyl chloride, CH2 = CHC1). This is accomplished by heating the 1,2-dichloroethane to 500°C over a charcoal catalyst to abstract HCl  

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