Structural and Solvent Effects in SN Reactions

Rates of SN2 Displacement of Alkyl Bromides with Iodide Ion in 2-Propanone (Acetone) Relative to Ethyl Bromide at 25° 

In addition to steric effects, other structural effects of R influence the Sn2 reactivity of RX. A double bond /3 to the halogen,6 as in 2-propenyl, phenylmethyl (benzyl), and 2-oxopropyl chlorides enhances the reactivity of the compounds toward nucleophiles. Thus the relative reactivities toward Iein 2-propanone are 

Possible reasons for these high reactivities will be discussed later (Section 14-3 B). 

6The Greek letters a, /3, y are used here not as nomenclature, but to designate the positions along a carbon chain from a functional group, X Cw- C8—C7—C,—C —X (also see Section 7-10). 

Exercise 8-12 Predict which compound in each of the following groups reacts most rapidly with potassium iodide in 2-propanone as solvent by the SN2 mechanism. Give your reasoning and name the substitution product by the IUPAC system, a. (CH3)3CCH2CI (CH3)3CCI CH3CH2CH2CHzCI 

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