Looking Back Reactions of Alcohols with Hydrogen Halides

15 LOOKING BACK REACTIONS OF ALCOHOLS WITH HYDROGEN HALIDES 

The principles developed in this chapter can be applied to a more detailed examination of the reaction of alcohols with hydrogen halides than was possible when this reaction was first introduced in Chapter 4. 

As pointed out in Chapter 4, the first step in the reaction is proton transfer to the alcohol from the hydrogen halide to yield an aUcyloxonium ion. This is an acid-base reaction. 

With primary alcohols, the next stage is an Sn2 reaction in which the halide ion, bromide, for example, displaces a molecule of water from the aUcyloxonium ion. 

With secondary and tertiary alcohols, this stage is an S l reaction in which the aUcyl-oxonium ion dissociates to a carbocation and water. 

The mechanisms by which sulfonate esters undergo nucleophilic substitution are the same as those of aUcyl halides. Inversion of configuration is observed in Sn2 reactions of aUcyl sulfonates and predominant inversion accompanied by racemization in SnI processes. 

PROBLEM 8.15 The hydrolysis of sulfonate esters of 2-octanol is a stereospecific reaction and proceeds with complete inversion of configuration. Write a structural formula that shows the stereochemistry of the 2-octanol formed by hydrolysis of an optically pure sample of (S)-(+)-1-methylheptyl p-toluenesulfonate, identify the product as R or S, and deduce its specific rotation. 

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Looking Back Reactions of Alcohols with Hydrogen Halides... 

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