Neighbouring groups can accelerate substitution reactions

Compare the rates of the following substitution reactions. Each of these reactions is a substitution of the leaving group (OTs or Cl) by solvent, known as a solvolysis. 

600 times faster than 3000 times faster than 1011 times faster than 670 times faster than 

Nearby groups can evidently increase the rate of substitution reactions significantly. Now, you may be thinking back to Chapter 17 and saying yes, yes, we know that —when we were discussing the mechanisms of substitution reactions we pointed out that a cation-stabilizing group at the reaction centre makes SnI reactions very fast for example— 

A sDlVQlysis was defined In Cffept ri7 as areaetion in Whjcfi fie solvent is also the nucleophile1.- 

In the four examples above, though, it is not at the reaction centre itself that the functional groups change but at the carbon next to the reaction centre, and we call these groups neighbouring groups. 

Netghbburi ng group participati on is occasionally called mcMmaric asd3tanee GFeeK enph/= neighbouddgr mer part). 

The mechanism by which they speed up the reactions is known as neighbouring group participation. Compare the reaction of this ether and this sulfide with an alcohol, 

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