Reactivities of Some Alkyl Halides

Sjyl/Sjy2 reactions Relative rates Reactivities 

The reactivities of alkyl halides in nucleophilic substitution reactions depend on two important factors reaction conditions and substrate structure. The reactivities of several subsfrafe fypes will be examined under bofh Sj l and Sj. 2 reaction conditions in this experiment. 

A reagent composed of sodium iodide or pofassium iodide dissolved in acetone is useful in classifying alkyl halides according to their reactivity in an Sj.j2 reaction. Iodide ion is an excellent nucleophile, and acetone is a nonpolar solvent. The tendency to form a precipitate increases the completeness of the reaction. Sodium iodide and potassium iodide are soluble in acetone, but the corresponding bromides and chlorides are not soluble. Consequently, as bromide ion or chloride ion is produced, the ion is precipitated from the solution. According to LeChate-lier s Principle, the precipitation of a product from the reaction solution drives the equilibrium toward the right such is the case in the reaction described here  

A reagent composed of silver nitrate dissolved in ethanol is useful in classifying alkyl halides according to their reactivity in an SNl reaction. Nitrate ion is a poor nucleophile, and ethanol is a moderately powerful ionizing solvent. The silver ion, because of its ability to coordinate the leaving halide ion to form a silver halide precipitate, greatly assists the ionization of the alkyl halide. Again, a precipitate as one of the reaction products also enhances the reaction. 

Before beginning this experiment, review the chapters dealing with nucleophilic substitution in your lecture textbook. 

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