The order of reactivity of alkyl halides towards nucleophilic substitution, for the same alkyl group, is
Correct answer: B. R-I greater than R-Br greater than R-Cl greater than R-F
- A. R-F greater than R-Cl greater than R-Br greater than R-I
- B. R-I greater than R-Br greater than R-Cl greater than R-F
- C. all four react at the same rate
- D. R-Cl greater than R-I greater than R-Br greater than R-F
Explanation
Reactivity is governed by the strength of the carbon to halogen bond, and that bond weakens down the group as the halogen gets larger, so the iodide breaks most easily and the fluoride hardly reacts at all. This outweighs the fact that fluorine creates the largest dipole. Iodide is also the most stable leaving group of the four.
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About Nucleophilic Substitution
Nucleophilic substitution replaces a leaving group in an alkyl halide when an electron-rich nucleophile attacks the carbon atom. The topic compares SN1 and SN2 mechanisms, including reaction conditions, substrate structure, solvent effects, nucleophile strength, carbocation formation and stereochemical changes, and distinguishes substitution from elimination.
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