Reactions of hydrogen halides

Oxetanes are much less susceptible to cleavage by nucleophiles than oxiranes, except in the presence of acids. Several types of acid-catalyzed nucleophilic reactions are described in the previous section, such as reaction of hydrogen halides to give 3-halogeno-1-propanols and various acid-catalyzed solvolysis reactions. Another example of this type is the reaction of thiourea with 2-alkyloxetanes in the presence of hydrochloric or perchloric acid to give excellent yields of 3-alkyl-3-hydroxybutylisothiouronium salts (equation 39) <67CR(C)(264)1309>. 

Alkenes. The reaction of hydrogen halides with alkenes is generally an electrophilic addition. It occurs by a variety of mechanisms and involves a carbocation... 

Addition reactions involve unsaturated compounds containing double or triple bonds, particularly C=C and C=C. Hydrogenation and reactions of hydrogen halides and halogens with alkenes and alkynes are examples of addition reactions. 

Chapter 11 deals with free radicals and their reactions. Fundamental structural concepts such as substituent effects on bond dissociation enthalpies (BDE) and radical stability are key to understanding the mechanisms of radical reactions. The patterns of stability and reactivity are illustrated by discussion of some of the absolute rate data that are available for free radical reactions. The reaction types that are discussed include halogenation and oxygenation, as well as addition reactions of hydrogen halides, carbon radicals, and thiols. Group transfer reactions, rearrangements, and fragmentations are also discussed. 

Whereas the reaction of hydrogen halides with borazines typically results in addition across the B—N bond to form the coordinately saturated trihalo rings, it has been observed that treatment of (HNBCOj with acetic acid (or acetic anhydride) effects a similar addition, along with chlorine replacement, but with a concomitant reduction in ring size to the dimer ... 

See Table 6.3. The mechanism of electrophilic addition is outlined for the reaction of hydrogen halides with alkenes. Carbocations are intermediates. 

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