Alkenes electrophilic addition reactions

Practically everything we ve said in previous chapters has been stated without any proof. We said in Section 6.8, for instance, that Markovnikov s rule is followed in alkene electrophilic addition reactions and that treatment of 1-butene with HC1 yields 2-chJorobutane rather than 1-chlorobutane. Similarly, we said in Section 11.7 that Zaitsev s rule is followed in elimination reactions and that treatment of 2-chlorobutane with NaOH yields 2-butene rather than 1-butene. But how do we know that these statements are correct The answer to these and many thousands of similar questions is that the structures of the reaction products have been determined experimentally. 

Well nee more details about alkene electrophilic addition reactions ahortly, but fia the present wc can imugine the readioa as takii place by Che pathway shown in Figure 5.4, Hie reaction begins when the alkene donates a pair of electrons from its OC bond to HBr to form a new C-H bond... 

Most reactions of carbonyl groups occur by one of four general mechanisms nucleophilic addition, nucleophilic acyl substitution, alpha substitution, am carbonyl condensation. These mechanisms have many variations, just a alkene electrophilic addition reactions and 8 2 reactions do, but the varia tions are much easier to learn when the fundamental features of the mechanisms are understood. Let s see what the four mechanisms are and what kinds of chemistry carbonyl groups undergo. 

Now that we understand the mechanisms of alkenes reactions, we can devise a rule that applies to all alkene electrophilic addition reactions The electrophile adds to the sp carbon that is bonded to the greater number of hydrogens. This is the rule you should remember because all electrophilic addition reactions follow this rule, so it will keep you from having to memorize which reactions follow Markovnikov s rule and which ones don t. 

---