Structure and SN2 Reactivity The Substrate

In Summary Determining whether and how a reaction may occur requires reasoning that takes into account the possible mechanism(s). The structural requirements of a reaction mechanism must be met by the substrates and reagents otherwise, they will not transform. Furthermore, when multiple pathways are possible, you should try to find information that allows discrimination among them (such as their relative rates or energetic favorability). 

Finally, does the structure of the alkyl portion of the substrate, particularly in the vicinity of the atom bearing the leaving group, affect the rate of nucleophilic attack Once again, we can get a sense of comparative reactivities by looking at relative rates of reaction. Let us examine the kinetic data that have been obtained. 

Branching at the reacting carbon decreases the rate of the n2 reaction 

What happens if we successively replace each of the hydrogens in a halomethane with a methyl group Will this affect the rate of its Sn2 reactions hi other words, what are the relative bimolecular nucleophilic reactivities of methyl, primary, secondary, and tertiary halides Kinetic experiments show that reactivities decrease rapidly in the order shown in Table 6-8. 

Relative Rates of 5 2 Reaction of Branched Bromoalkanes with Iodide 

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